My wife has been telling about a "hissing" noise that is coming from under her hood for last couple months. I drove the car and around 35-40 mph you can hear the best I can say a "hissing" noise? What could this be? Its coming from front, and it seems to occur only round the 35-40mph area? I thought it could be vacuum and had her rev motor while I listened under hood? Nothing heard, so what ever it is, is only happening when the car is in motion? Thanks for the input guys!

Does the car have a CAI on it, or stock induction?

Hmmmm I know I'm getting older but @ 35mph I wouldn't be able to hear a vaccume leak under the hood! :lol: Under the dash yes, but not outside the car...

Have you checked for any codes??? There's nothing else funny going on with the car like the AC vent on the driver's side not working right or the speedo sticking say at 35 mph??? Heck you might even have a plastic gorcery bag stuck up inside your radiator...

Keep us updated.

Hmmmm I know I'm getting older but @ 35mph I wouldn't be able to hear a vaccume leak under the hood! :lol: Under the dash yes, but not outside the car...

Have you checked for any codes??? There's nothing else funny going on with the car like the AC vent on the driver's side not working right or the speedo sticking say at 35 mph??? Heck you might even have a plastic gorcery bag stuck up inside your radiator...

Keep us updated.
:rofl: That was funny! I can't hear anything anyways let alone a vacuum leak. I would have guessed that it was the air intake sucking up the air, but usually that only happens when you get on it.

My wife has been telling about a "hissing" noise that is coming from under her hood for last couple months. I drove the car and around 35-40 mph you can hear the best I can say a "hissing" noise? What could this be? Its coming from front, and it seems to occur only round the 35-40mph area? I thought it could be vacuum and had her rev motor while I listened under hood? Nothing heard, so what ever it is, is only happening when the car is in motion? Thanks for the input guys!

Its a conspiracy, your wife is saying you need to get her a new C6! Are you sure its a non metalic noise? I can't imagine you being able to hear a valcuum noise? If its a metalic noise, I would start looking at the other items!

Does the car have a CAI on it, or stock induction?

I was thinking the same thing. Great question

Is it a constant noise or does it come on and off periodically?

There is a thin hose attatched to the intake manifold. I found this out when I swapped mine out. I didn't put it back on tight enough and it came off. It was an umissable hissing sound. It took me some time reaching directly around the back of the intake but I got it on securly. I was not about to take that manifold off and put it back on.:eek:

Could be all of the above. I'm betting on a CAI/throttle body whistle because you can hear a vacuum leak at idle. How about a catch can? One of my customers had a whistling catch can.

could just be a vacuum hose. That would be my guess at this point!

Terry