This has been going on for about a month and I’m at a loss. I’ve searched YouTube and Google and there’s not many videos or discussion about this type of noise. The car is tuned for 25PSI and it overboosts to 26 at WOT before tapering off. The noise is inaudible when revving while parked and while it’s in vacuum but it starts at 10%+ throttle at around 5PSI and gets higher pitched and more rapid at high boost. I replaced the stock BPV with ZZPs billet one but that wasn’t the issue. I inspected the turbo compressor as best I could, hard to properly check it due to the small inlet on the K04 and the location of the turbo, but I couldn’t feel any shaft play and the turbo still spins perfectly with my finger after a month of this noise happening. The noise hasn’t changed at all. Does anyone have any idea what it could be? Wastegate actuator issue? Simply a small boost leak that I couldn’t find? YouTube links to sound: https://youtube.com/shorts/43qaXvysOxg?si=LOz7QEUnja7iFx8O
https://youtube.com/shorts/ikWOI4wumEM?si=Uco5boXvYEl7VMoL

 

I had a similar issue and it was caused by shaft play on my stock turbo. Might be a sign it’s on the way out if you find nothing else. It wasn’t noticeable when I inspected it on the car but when I upgraded the Turbo it was pretty clear it had been touching the housing a bit and had play

 

I hope that’s not my case as well, I only got the car at the end of April. I’m still not burning oil and the compressor wheel still looks fine, housing is bone dry, and I’m still making full boost. It just overboosts at WOT and makes that weird chirping noise. I took a video of the wheel spinning after giving it a whirl with my finger and it doesn’t wobble at all, albeit of course that’s a fraction of its actual running speed. But all in all there’s no visible damage. I did find another thread of someone’s cobalt making a similar noise and evidently he just had a boost leak, and someone replied to that thread saying that happened to them when one of the turbo to manifold bolts was loose. What other issues did you have?

 

Also, this noise started about a month ago and hasn’t changed. I figured if the turbo were on its way out the sound would’ve gotten worse by now and I’d have other symptoms like burning oil.