Hey everyone,
Installed a couple of days ago my new HKS Hi-Power single exhaust. Sounds great, love it and all, but I am noticing a bit of a high pitched squealing rattle at idle ONLY. I barely ever heard it, but am hearing it more and more. Any suggestions? I used a new donut gasket from the dealer when installing.. And it sounds like it's coming from that area. I ran into an STI friend of mine who has the same exhaust and he said might be the hangers. Suggestions anyone?

UPDATE:
Alright so we went under the car today. Here's all the information we have...

The noise only happens when the car is idling and is warmed up (like a good while..Not just starting up)

The noise is not fully consistent..It'll vibrate/high pitch rattle for a bit...stop..then louder then stop then again then stop..or do it for a long time..or do it for the whole red light.

Standing NEXT to the car...It sounds like it's coming from where the exhaust connects to the cat.

Laying under the car, it sounds from the pipe itself, but mostly from the muffler can.

We looked at everything and nothing seems to be hitting or touching at all, though the exhaust does vibrate a decent amount.

We wedged the rubber mallet to the exhaust pipe and pushed up half an inch and the sound went away..For a bit. Before it came back.

We're thinking it MAY need to break in a bit more, or something is rattling inside the exhaust. We're really not sure.. It's the most annoying thing at red lights and makes me want to just run from my car....

Is everything tightened?

mine rattles like crazy too. turns out to be the gas tank heat shield. i'm gonna have to take my exhaust off again to bang that thing in.

yeah on mine the piece where the ground connects to the exhaust hit that heat shield (which frankly i think sucks :lol:) so i had to do a little convincing with a pair of pliars

also some hangers can hit the rear diff. its worth looking into that too

Ugh all this for an exhaust. lol. Hmmm.. I'll take a look into those then. Thanks guys.

Alright so we went under the car today. Here's all the information we have...

The noise only happens when the car is idling and is warmed up (like a good while..Not just starting up)

The noise is not fully consistent..It'll vibrate/high pitch rattle for a bit...stop..then louder then stop then again then stop..or do it for a long time..or do it for the whole red light.

Standing NEXT to the car...It sounds like it's coming from where the exhaust connects to the cat.

Laying under the car, it sounds from the pipe itself, but mostly from the muffler can.

We looked at everything and nothing seems to be hitting or touching at all, though the exhaust does vibrate a decent amount.

We wedged the rubber mallet to the exhaust pipe and pushed up half an inch and the sound went away..For a bit. Before it came back.

We're thinking it MAY need to break in a bit more, or something is rattling inside the exhaust. We're really not sure.. It's the most annoying thing at red lights and makes me want to just run from my car....

it really sounds like the same as mine. get under there and move your exhaust back and forth and see where it hits. the black paint on the pipe should also be rubbing off in the spot its hitting. mine hits the gas tank heat shield on the passenger side.

Wait you have the HKS Hi-Power single? Just double checking. We'll go look at that now.

Nothing is hitting anything. At all. And it only makes sense that if it WAS hitting something, it would be a constant noise... as opposed to ONLY when it gets really warm, and the noise goes on and off from time to time.. right?

yes i have the HKS Hi-Power. i'm telling you man, mine does the same thing. only when its warmed up and only when it idles. i have the suspicion its bad motor mounts that is making it do it. it hits the gas tank though.

Motor mounts? How could it make that kind of noise in the exhaust? and it hits the gas tank? Well I'll pull it off and take a peak. Thanks for the heads up.

I looked at Zelse's exhaust and there's no way it's hitting anything. I can see where the gas tank heat shield is and there's plenty of space between that and the exhaust. There is no black paint rubbing off anywhere. The sound is heard from the can and throughout the pipe. Pushing the pipe with a rubber mallet to quiet the sounds makes them go away for a moment, and the sounds come back in, though not as strongly. We pushed up and down and away from the passenger side and it's the same result.

From your description, your resonance problem is either within the exhaust piping or a heat shield attached to the car.

Think of the whole thing like a loudspeaker that is rattling your dishes at a certain bass note.

I'd have a look at the car first...

Get a mechanic's stethoscope and a long screwdriver (or metal bar).

With the car running on jackstands, you're gonna have to wait for the rattle to start.

Poke (push to hold) every metal piece in turn under the car from the front to the back. When you get to the right piece, the noise will stop!

The purpose of the stethoscope is to more quickly isolate the general area of the noise.

Re-secure the offending heat shield, or put on some rubber washers to isolate the vibration. If this doesn't help, then add mass (drill a hole in the shield and put in a nut/bolt for weight) to change the resonant frequency.

If the rattling is in the exhaust, then find the offending joint and change / add gaskets. Again, you may have to add mass (hose clamps and metal scraps) to change the resonant frequency.

This may take a while, but will be worth it.


Note: The root cause of your excess vibration should not be ignored.... Check you engine mounts and the PPF.

Hmm.. Very good options there. Thanks for the help on that. And I didn't think of it before...but I very well could've been hearing the sound before but much quieter, right? I'll take a peak.

Mine did the same thing when new(OBX) and it was one of the hangars rubbing against the rear diff...some channel locks and alot of elbow grease i bent it out and have no noise now also check that you don't have loosness on the springs at the cat....if those arent really tighten down they can vibrate backa and forth causing a noise...

...That actually makes sense. I'll check into that asap. Thanks for that!

it really sounds like the same as mine. get under there and move your exhaust back and forth and see where it hits. the black paint on the pipe should also be rubbing off in the spot its hitting. mine hits the gas tank heat shield on the passenger side.

Thread revival! Having the same issue with my HKS rubbing the gas tank heat shield. It is not caused by my motor mounts, they have been replaced. I also have polyurethane hangers. When the rattle first started I managed to get the exhaust to shift a little to stop the rattle but once I put a few more miles and heat cycles on the exhaust it moves right back and starts again.

Could having this paired with my agency power mid pipe cause the exhaust to sit a little closer to the left putting it to close to the heat shield? I noticed in pictures that the metal hanger welded to the AP midpipe is shaped different than RB's and BHR's midpipe.

Anyone else have the HKS high power have this same problem and come up with a solution besides banging in or removing the heat shield on the gas tank?