absinthe minddgrl

Hi guys,
I have searched through the posts and can't seem to find my particular problem.
I purchased an AT 2008 about 10 days ago. 47K miles.

I have a weird problem that I can't find an explanation for.
At about 55 MPH (I'm sorry...I didn't look at the RPM's, but it's usually on the highway 5-6 gear) and all the way up to about 68 MPH the engine makes a low frequency rhythmic oscillation sound. It is very steady. It doesn't seem to increase or decrease within that speed range, just stops above and below those MPH.
Before and after the engine runs smoothly and seems to have full power. It also seems to run smoothly during except for the very smallest (almost imperceptible lurch at each "cycle" of the oscillation). It's a quick turnover of the sound very steady, about 1.5 seconds between "cycles". It isn't the tires.
If I was going to equate it to a sound, it reminds me of the sound an electrical transformer makes, if you've ever been near one...or maybe the Tractor Beam in Star Wars (sorry I'm a nerd)
I hope this all makes sense. I am scheduling her for a checkup at my local Mazda dealership, but I wanted to get a heads up on what to possible expect them to tell me.
If I just missed it in the search and there is a topic addressing this, please direct me to the link and forgive my poor search skills.


I have the coolant light issue, as well, but after reading through the many posts on this, I know that it's just the sensor and am going to get it replaced.

Thanks in advance,
Absinthe Minddgrl

dynamho

Nicely written.
The described symptoms are a new one for me, so I can't help.

Shooting in the dark, it feels transmission related.

RX8Soldier

iTrader: (24)

Is there a way to tell where the sound is coming from (driver front/rear, passenger front/rear, engine, etc)?

PeteInLongBeach

Why would you assume that? At the indicated mileage, it would be extremely unlikely that the transmission is slipping.

It could be a motor mount, exhaust system resonance, or some other loose part causing the noise.

Keep in mind that the motor with the A/T is turning quite slowly at 55 mph in 6th (about 1800 rpm), so the mild engine vibration at this speed could cause some other component to resonate.

zoom44

absinthe are there any changes to the stereo system from stock that you are aware of? any other changes to the car that might have added anything electrical/electronic? extra lighting etc?

dynamho

I didn't assume anything.

My post had two disclaimers.

absinthe minddgrl

Okay...
1. The transmission doesn't "feel" weird...I had a lot of transmission problems with my previous car and I don't get the sense that there is any slipping...but I've only been driving the car for 11 days, so all of it's sounds are new.
2. to me the sound definitely sounds engine related, dead center when I'm driving. I really listened today (radio off of course) and it seemed to generate right in the middle.
3. It is a very steady sound at the mphs described above and then abrubtly ends at about 69 or 70. That's true about the rpms, Pete...nothing over 1800 or so at that speed, I even goosed it to see if I could get the rpms to jump and notice the sound before it hit the threshold, but couldn't make it happen.
4. it doesn't seem to be vibration or something loose, it feels mechanical. But I'm definitely not a mechanic so that is my purely uneducated female intuition.
5. as far as I can tell everything is stock. I bought it from Carmax and the disclosure didn't mention any changes to the regular touring package.

I think I addressed the questions...I really am babying her until I know what the deal is. Checking the oil regularly, keeping an eye on the coolant. I just don't want to think I've got a Lemon.

Easy_E1

iTrader: (2)

Put the shifter into manual mode. I would down shift to the next lower gear at those speeds to see if the harmoninc sound changes. Sounds like an exhaust pressure resonance to me.

absinthe minddgrl

Okay...I am a little nervous as I haven't actually tried the manual mode, yet.
Keep it at the same speed and see what happens in maybe 4th gear?

dynamho

I found this write-up about TCC (Torque Converter Clutch). Not sure if it will become relevant.

http://www.edmunds.com/car-technolog...rticleid=43836

"The Lockup Torque Converter

Because the only connection between two sides of a torque converter is a fluid connection, there is always a little slippage, running from about 2-8%. To increase efficiency and gas mileage, most modern automatic transmissions also have something called a lockup clutch (aka, torque converter clutch).

It works like this. As the speed of the car nears 40 miles per hour, the highly pressurized transmission fluid is channeled through the transmission shaft and activates a clutch piston. This metal pin locks the turbine to the impeller, in effect bypassing the torque converter. It remains this way until the vehicle slows below 40 mph, at which point the clutch piston disengages and the torque converter kicks in again. Simple, right?"

------------

Just a hypothesis here, nothing more.

Perhaps it's a lazy clutch lockup, solenoid if electrically activated, or a sticking valve? It's trying to lockup the clutch at the speeds you mentioned. The "2-8%" mentioned in the article feels like the "almost imperceptible lurch" you mentioned. The torque converter is mated to the center of the engine between it and the transmission and anything going on there can be felt to originate from the engine I think.

I was just reading that many erratic lockup issues (if that is the issue) can be solved by simply replacing ATF, filter, and adding something called LubeGard to free the sticking valve. The post was made by a supposed transmission mechanic w/ 40 years experience. (src: http://answers.yahoo.com/question/in...4023011AAYku6L)

Hesselrode

iTrader: (3)

I agree Easy E1, does it only do it in the one gear or does it do it as the gears change continuous. put the car into neutral, does it still do it? when you run hard does it do it or under normal driving or both? Try putting into neutal and take your foot off the gas and listen. then try reving to 2k, 3k, 4k. Does it still do this sound? if you put into neutral and it goes away then it is the transmission making that noise probably. Also, putting into neutral makes your rpms go down, so could eliminate anything engine related.

REDRX3RX8

I've got a 07 6spd auto GT with 27k miles and 4.5 years.

My auto slipped some ( engine reved but not much movement) a few weeks after I bought new.

They drained a quart overfill which worked until I over heated it on track day.

Even driving to the dealer ( limping in 3rd safe mode), it never made any noise whatsoever.

My car and nearly ever car I've owned makes a normal but horrendous whine from the rear differential when under light load at 50-60 mph.

So go test drive at 50-55 mph with constant speed, then push gas down about halfway to get load but not noise so you can listen to the rear wheels, and see if that's it.

Also, drain the rear differential, and put something like 1.9 quarts MObil 1 synthetic gear oil 75w90 until it runs out then put plug.

At 3500 miles my differential had lots of metal mud, and sometimes people have differential issues at your mileage.

PeteInLongBeach

From the symptoms described, I don't believe it is transmission or differential related at all. I would get the car up on a lift and inspect the underbody, exhaust system, heat shields and hangers for integrity or any obvious damage. I would also inspect the passenger side motor mount for any signs of deterioration, as this is known to perish from the exhaust system heat and can cause vibration.

StreetGT

It sounds to be like it has to be mechanical, as cool as resonance is, I would be surprised if it could be as consistent as she says it is being. Just stopping, after 68mph seems suspect to me..

Rx8 transmissions are wacky, they had to build them.. differently to accommodate the high rpm's. I doubt it will be a big problem.

In your first post absinthe (I love absinthe...) you mention that you have full power before and after, are you saying there is a power loss at that rpm/speed range? If so then a whole new genre of problems could be the culprit.

Good luck.

PeteInLongBeach

Other than reports of synchronizer issues (which might also be attributable to abuse, clutch pedal bracket or clutch master cylinder failure), there is little "wacky" about the manual transmissions.

But whatever, she has an automatic, and there is nothing wacky about that either. It's a relatively conventional 6-speed aisin transmission, and there are very few reports of any problems with them on the forum.

absinthe minddgrl

StreetGT,
Tried to determine if it was just stopping or diminishing incrementally after 68 miles or so....really does seem to be completely gone after 70 mph. Was in some slow and go traffic on the highway today...speeding up to 75 slowing down to 45 and it really did seem to be consistent and very noticeable between 55 and 68. There is no change in performance that I can tell when it's "cycling" (that's the name I've given it when I'm driving and it's happening), just a slight...oh so slight...hesitation with each "cycle". Well, I guess that hesitation is an example of diminished performance, but it really doesn't feel any worse than when the car downshifts to accommodate my driving in traffic.
I'm thinking I'm just gonna get the tech to ride with me so I can see - "THERE" - when it happens.

REDRX3RX8

Most car problems can be narrowed down with logic even if you have minimal experience.

I threw out the whining rear end because even experienced people sometimes think the noise is on the other axle.

One thing you can do to shoot down my theory of differential is to put your auto in manual 5th gear and see if it still does it at the same speed, and then try in 4th.

In other words, if its anywhere on the engine it should be rpm related by tach instead of mph of 55-68 which has constant relationship with diff noise.

I've also had some Chrysler cars that had a real annoying wa-wa-wa noise in the front bearing that was very speed related.

absinthe minddgrl

Hey guys, had a friend that has experience with RX7's and 8's take a look at it and he said that the rear drivers-side wheel looked like at one time it had had a blow-out and that the outer rim had been buffed smooth but not replaced. The inside rim was really chewed up. He thought, perhaps that would account for the sound I am hearing.
Took it to the dealer and told them to check that out...they balanced the tires and gave it back to me...now, it's doing it even worse. So, I think it's safe to say he's on the right track. I'd like a new wheel, but I'm not sure how much I'm gonna have to dig my heels in for that.

Taking it back in on Friday to have them look at it again....*fingers crossed*

Rotary_Illiterate

OP- I actually have the same noise in my car. It didnt happen until they flashed my ECU. I have become acustomed to it. I coudlnt have described the noise any better, it's identical to yours.

RX8Soldier

iTrader: (24)

members sell used OEM wheels all the time, usually for ~$100 per rim. Check out the "For Sale" section

absinthe minddgrl

I guess I might eventually...but my god, it is driving me crazy!!!