Bought my car about 3 years ago with a blown turbo. Since I was at school, had a local euro shop put a new ko3 in. Since day 1 with the new ko3 it makes an ear peircing squeal above 10 psi of boost. Ruled out the by-pass valve and boost leaks. Saw on the s4 forum that some experience the wastegate rod rubbing the heat shielding on the frame so I tried to move that the best I could with the turbo in place. With 35k on the turbo still have no problem peaking at 19 psi and holding 14-15 to redline. With a stereo upgrade in progress I was driving with the passenger interior door panel off and could hear the turbo at low boost or when the engine has a load, making a faint noise similar to a bad wheel bearing (rubbing metal), which I believe this noise turns into the load squealing. My next step just short of doing a upgrade is taking the compressor housing off to clean up any casting burrs or imperfections. Anyone have any suggestions what to look at.

what kind of exhaust are you running? i am currently having a similar situation with my turbo "squealing." from what i found out about my car is that it's my exhaust. i have a neuspeed g2 and it's known to have a bad scream at full boost over 5000rpms. this is just a heads up for you if you have the neuspeed exhaust.

I do have the neuspeed exhaust, do you know what about the exhaust is causing the screaming. How much boost are you running

ah HAH! yeah, i don't know why, but Silvant (on az, dont know if he's here too)told me he had the Neuspeed gen 1 and they were "known" to scream at full boost after 5000rpms. I'm running a k04 and it's really REALLY loud once it hit 15-18psi at 5000rpms.

I think that there is just too much turbulence and/or backpressure in the exhaust system. I plan on removing the middle muffler and replacing it w/ a resonator. Hopefully this will be a cheap fix. If not, a Milltek exhaust will be on it's way.

is it a k03 sport or a regular k03