Exhaust weird sound - bad tips or boost leak?

[jmz135]

After installing a aFe axleback I starting hearing a strange noise when opening up the throttle. Basically whenever I go WOT there is an annoying horn sound. Not nearly as loud as some of those early berk models, but similar type of noise. I've been doing some research and some people are saying it can be caused by a boost leak, and it only happens at WOT because that is when the boost is the highest and causes the noise.

I got a boost gauge and hooked it up to my car last night and did a few runs. If I shift it up to 4th when I'm going 20mph and floor it, the boost immediately goes to 7.5-8.5 (up to 9.5ish when in sport mode), but the noise doesnt start until about 4k RPMs.

The other half of my research indicated that it could be poorly welded tips causing a whistling/horn sound. Does this sound more like a poorly made exahust, or a boost leak? I have some replacement tips I can put on, but don't want to pay $100 to have them cut and installed unless I think it will fix the issue...

[edisapimp]

Where is the noise coming from? Is it coming from the back of the car (near your new muffler), or the engine bay (near your turbos)?

Have someone drive near or behind you while you are doing these WOT pulls and maybe you can localize the noise to come up with your answer. The two sources you are suspicious of are pretty far apart in location, so this might be a good place to start.

[jmz135]

Ok - I'm pretty confident it is coming from the rear of the car. I wasn't sure if that was a foolproof way to tell with a turbo car...wasn't sure if the exhaust might be amplifying something coming from the engine bay.

Does a boost leak typically only happen towards the high end of boost, or will it always be present?

Also is roughly 8psi normal for a stock 135i?

[edisapimp]

Originally Posted by jmz135

Ok - I'm pretty confident it is coming from the rear of the car. I wasn't sure if that was a foolproof way to tell with a turbo car...wasn't sure if the exhaust might be amplifying something coming from the engine bay.

Does a boost leak typically only happen towards the high end of boost, or will it always be present?

Also is roughly 8psi normal for a stock 135i?

Boost leaks come in all shapes and sizes. But the short answer to your questions is "Yes to all."

[jmz135]

Originally Posted by edisapimp

Boost leaks come in all shapes and sizes. But the short answer to your questions is "Yes to all."

Ok thanks man, that is very helpful. I'm leaning towards it being a exhaust piping issue, maybe something with resonation.

I know every situation is different, but does it seem possible that the tips are causing the noise?

I spent ~$600 on this axleback and dont want to have to throw it away. I can have someone cut off the tips and install the new ones I have for roughly $100, but dont want to waste my money if it's a different issue. Not sure if there is any way to tell other than cutting off the tips and seeing if it still happens without them...

[edisapimp]

Well consider the variable here. You had no noise.. you changed the exhaust, now you have the noise. Look for horses not zebras. Where did you get this exhaust from? Is it used? Can you ask the company for assistance? If it's defective, you shouldn't need to alter it to make it work, you should get a replacement or get your money back.

[ShocknAwe]

Originally Posted by edisapimp

Well consider the variable here. You had no noise.. you changed the exhaust, now you have the noise. Look for horses not zebras. Where did you get this exhaust from? Is it used? Can you ask the company for assistance? If it's defective, you shouldn't need to alter it to make it work, you should get a replacement or get your money back.

x1000

[jmz135]

Originally Posted by edisapimp

Well consider the variable here. You had no noise.. you changed the exhaust, now you have the noise. Look for horses not zebras. Where did you get this exhaust from? Is it used? Can you ask the company for assistance? If it's defective, you shouldn't need to alter it to make it work, you should get a replacement or get your money back.

I agree. I bought it new from aFe. I sent a message to their customer support a few days ago and they haven't responded.

[edisapimp]

Originally Posted by jmz135

I agree. I bought it new from aFe. I sent a message to their customer support a few days ago and they haven't responded.

Okay, well it's Friday, so give them the weekend and Monday to get back with you. Stay the course, be a little persistant but not obnoxious. Try your hardest to speak with a person over the phone if you can. People are a lot less apt to blow you off when they hear your voice versus read your words. In the mean time, I would visually re-inspect the way the pipes are fitted. Maybe check to see if you can see anything loose in the plumbing, can you feel any exhaust leaks from near gaskets.. This type of thing. Could be simple, but if you exhaust (no pun intended) the obvious, then you may be left with a defective muffler.