I have a 2009 Cobalt SS LNF with the stock k04 turbo. Car also has zzp intercooler, zzp 3.25 cai, opel injectors, zzp charge piping, zzp rad and coolant tubing. What I'm worried about is a noise I'm getting, only under full boost. Car is tuned with a 1st boost reduction (only makes maybe 4-6 psi, 24-25 in every other gear). When the cars cold and has been driven for a few minutes, anything about 14-16 psi and there's a chirping noise from the passenger side up front, where the turbo is located on these cars. I first thought it was a wastegate or actuator issue but I have no issues with boost regulation. Car drives great, no codes. When its full warm the noise is there but much, much quieter. I also thought possible timing chain, but as mentioned first gear has boost reduction and it does not make the noise in that gear while WOT which it should if it was timing chain related(plus i've never heard the chain rattle even on start up after sitting for a few days. I plan on swapping to a z54 turbo eventually but curious if anyone has any information on this. Thanks!

 

Really hard to say, I'd visually check the turbo inlet for damage or excess oil. Then check for shaft play, a bit in and out (direction of the turbine shaft) is normal, but towards the housing should be very little if any.

 

As ECaulk mentioned, check for excessive end-play. "Chirping" could be the compressor wheel and compressor cover trim making contact, which obviously is not good. Look for signs of material displacement on the end of the compressor blades, and check for that shaft play. If the thrust bearing gets wiped out, you'll have excessive end-play (thrust).

If everything feels fine then it could possibly be the wastegate shaft/lever may be on the tight side when cold, and the TH might grow more than the shaft allowing for additional clearance at temperature, which is why it's not as pronounced. If you disconnect the wg can can you freely move the shaft and lever?

 

I have already checked the turbo for shaft play and there’s almost none at all, spins freely as well. No visible scoring on the housing. I suspect the bov like you had mentioned. Oil is clean as well, I usually check my filter for metal particles with a magnet every oil change.

 

That’s what my turbo started to do sorta squealing when it ramped into boost. 15ish psi is when it started. Got less noticeable once it was hot. When I pulled the turbo it had some shaft play. Didn’t seem like it when it was installed.