I have a MY2008 S2k with a test pipe and SoS stage 2 SC kit. After its first dyno-tune I noticed that there is now a prominent, low whistling/howling sound while applying a very small amount of throttle. It sounds almost like some kind of exhaust resonance, but I'm really not sure. Releasing or increasing the throttle causes the noise to cease, and it was not present for the drive to the shop with a base map from SoS.

I would probably just overlook it, but unfortunately the partial throttle required to cruise at highway speeds seems to be just right to make the sound occur.

Has anyone else here encountered this before? Any advice?

 

could be the bov/recirc valve opening and closing... if you are part throttle or idling the valve would be dumping... when i swap my bypass valve to VTA, i notice the "hair dryer" sound quite often...

have you changed anything on the setup?

 

Mine does the same under light throttle, it's just the bov dumping and probably open just enough for it to whistle.

Advice: Enjoy your cool new boost noises

 

This would be my guess as well. I've heard of this happening on other supercharged vehicles as well.

Do you have a boost gauge? If you monitor that while you're cruising and look at it while the BoV is modulating that may be an indicator. I'm not entirely sure as I've never driven a SC vehicle.

 

For those of you saying it's the BoV, I should mention that the sound does not seem to be coming from under the hood. It's irritatingly difficult to determine where it is while driving, but sometimes I'm convinced it's at the test pipe, and other times it seems to be from further back. In any case, thanks for taking time to respond with advice.

 

Jack up the car and check the exhaust for leaks. Give everything a once over and tighten all the bolts a bit. Make sure there isn't like any gaskets that exploded or anything

 

With my current exhaust (J's Racing 60rs), I had a whistle sound (but not really high pitch at all) when I ran a 63mm TP on the OEM header. The sound was only present during certain load/RPM conditions. I had a shop check for leaks when I had an O2 bung welded on the TP, and that wasn't the issue. Resonance of some sort is the only thing I could think of...

Recently, I installed the PLM header, and at the same time, I bought their 70mm TP. The whistle seems to be gone, as I've not been able to reproduce it at any load/RPM combination.

As others have suggested, check for leaks. If there aren't any, then it's fine. If you can't live with the sound, the cheapest thing to try is a new TP.