Very weird high-pitched noise from upper part of engine
 

Hello all, this is my first post in this forum outside of random "for sale" threads. To make a very long story short, I have a 2009 Touring w/ MT, a Mazda re-man engine that was installed less than 1000 miles ago(the odometer shows 50,xxx miles currently). During the install, the following mods were also installed: BHR Ignition, BHR Engine mounts, Racing Beat header, Agency Power cat-less exhaust system, Koyorad radiator, K&N air clean filter, Agency Power steel braided brake lines and steel braided clutch line, Agency Power Sway bars(front and rear), Agency Power adjustable links. I've also replaced the MAF with a brand new new one from Mazda, as I've gather that is generally the source of most issues with this car. I've already checked vacuum lines according to the Mazda workshop manual(except the Purge Solenoid, since it will take some delving to reach it), and everything seems to be holding correctly. RPM at idle is right between 810-840(which I've also gathered is where it is meant to be), there are NO CEL's, no pending CEL's, STFT% varies between -1 and +1, and LTFT% is hovering around +5%. Power appears to be good, with no hesitation/sputtering/bucking, etc. anywhere in the RPM range.

The issue I am currently having, is a very loud, distinct high-pitched squeak/whistle from what seems to be in the area of the UIM. At idle, I can hear the noise inside the cabin with the windows closed, but it does seemingly go away(or engine and exhaust drown out the noise) anywhere above 2,000 RPM. Although, while driving between 3,000-5,000 RPM, it sounds like there is a scratching and/or rattling noise coming from somewhere in the engine bay. The sound is definitely more distinct when accelerating or decelerating in the 3k-5k range, but there does not seem to be any other symptoms apart from annoying noises. The even more odd part about my entire situation, is that when I remove the oil filler cap or the oil dipstick while the engine is RUNNING at idle, there is quite a large amount of suction being applied to them, and does take quite a bit of force to remove them. And once either of them has been taken off, the loud whistle that I'm complaining about goes away completely. I will attach a video of the noise shortly, as well as me pulling the dipstick out, to show the noise quickly disappear.

I've been under the assumption that whatever this noise is, is tied to the vacuum system, since any change to the system causes the noise to go away. Any one have any ideas? Thanks in advance!

Video link:
https://share.icloud.com/photos/07LK...ago_&_Evanston

I don't know but for some ideas if it were me I'd check oil levels and maybe swap oil filter since it seems connected. Might be way off but it's the first thing I'd do. (Assuming there is no vac leak)
Good luck.

Thank you for the suggestion. I'll have to get it up on a lift and take a look. Although, the car was not initially making the noise for the first few weeks after the engine was installed, and came out of no where one day after I started it up. I also forgot to include in my original post, that the noise in question presents itself about 15-20 seconds after a cold start, if that helps. I've already convinced myself(for better, or worse) that it is indeed a vacuum leak of some sort. But it of course doesn't hurt to check the basics, so again, I do appreciate the help!

If anyone else has any other suggestions after watching the video, I’m all ears! Since I’ll have the car in the air sometime this week, I’d like to be able to check for any other possible solutions while I have the chance. Thanks!

I just watched your video, that's hands down the weirdest thing I've seen on an RX-8 yet! Midway through the video, when you took off your oil cap, it looked as if oil was all the way near the top. Seems to me that you could have overfilled the oil and something funny is going on in your oil system. The RX-8 uses a dry sump so overfilling the car can cause problems. Have you tried removing the air box and hose and checking to see if oil has gotten into your throttle body? I'm all out of ideas if this isn't the cause of your issue though. That is really weird stuff going on in your car haha I hope you can figure out the cause of it because I've personally never seen anything like that happen before. It still seems related to an intake issue but if you can pinpoint the exact spot the sound is coming from that might help as well. If not, the only other thing I could possibly think is the back pressure isn't right. Is the Cat recently replaced or still in good shape?

Did some more digging and I believe it could be a crankcase pressure problem. The newer RX8's (like yours) have a different setup from the 04-05 cars I'm used to working on. Replace the PCV valve and inspect the PCV hoses for damage, clogs, cracks, or being misrouted. Also, still check your intake for oil and ensure all your hoses are routed correctly. That's all I got for now.

Thanks for the additional input- it’s my suspicion that it may be the PCV valve as well. Since it’s one of the only parts that I haven’t diag’d yet, and the noise in question seems to be coming from the same area. I know that you mentioned that you have limited experience with 09’s, but would you happen to know if there is anyone of testing the PCV valve without removing the UIM? Or maybe someone else on this forum knows?

Unfortunately wouldn’t be me. I’ve never even seen an S2 in person lol. Hopefully someone here knows how to help with that.

Ya closest I've seen in person is the 40th anniversary. A buddy has one.

So I was able figure out what the issue was- the vacuum lines coming from the intake hose! Since the S2 re-routed one of the vacuum lines directly into the lower intake manifold, Mazda plugged the vacuum hole/input facing directly up on the intake. Of course the long-time rotary technician who built my car is far more familiar with the S1, so he didn't even think about it while putting the intake on. Either way, I shifted the 2 vacuum lines over one hole, low and behold, the noise disappears and I hear the car adjusting itself immediately. I'm not sure which hose was in the plugged hole, and not receiving any vacuum, but I imagine it had something to do with the oil system. Everything ran fine, minus the weird noises of course, before the fix, but I can now feel a considerable power increase across all RPM ranges, as well as a considerable reduction in noise from the engine and exhaust(in a good way). Luckily, I was already using a pretty strong 100:1 ratio of Idemitsu Rotary Pre-mix, just to be safe, since it is a newly re-built engine. I'm still wondering what it is about the oil system in the car that caused this to happen, but I still do appreciate the help guys, so thank you anyway!

Great news! I'm glad this got fixed for you. Now you can actually enjoy that beautiful car.