Kind of sounds like a vacuum leak or some kind of boost leak some where.. Doesn't seem as if performance is affected or any boost is being lost according the the guage.. Have no idea where to start, i tried to tighten intake hose clamps.. Im trying to upload a video.

 

Do you have turbocharged Cobalt or supercharged?

 

supercharged. sorry I should have included that info..!! im trying to upload a video tonight! I hope that ill be able to, my phone wouldn't let me upload it.

 

You can hear the noise a little before 5k RPM at full throttle. Really hope it will be an easy fix..

 

Honestly all I could hear is supercharger wine in that video which is perfectly normal. Have you done anything different with your intake?

 

I have owned the car for almost 8 years now and this noise just started happening this past week. no, I have had the k & n on it the 8 years. all I have done is cleaned the intake multiple times.

 

What I could hear sounds like supercharger whine. If I can find a decent set of headphones lying around may try to listen a bit closer. You are referencing the whine that comes in at 4,500 rpm correct?

 

Okay that would be awesome, its driving me insane. Yes it is the noise that you hear around 4500! its like a whistling/ vacuum noise, maybe the video isn't the best quality but it definitely doesn't sound right in person.. :/

Also, I tried replacing the 2 vacuum hoses going from the bypass valve to the supercharger, and from the bypass valve to the boost control solenoid as they were starting to develop some cracking, also tested to see proper function of the solenoid and it seems to be working correctly.