i have a 2007 h3 base 94k on it everything works great but i noticed a high pitch humming noise. i intsalled a k&n intake and thought it was that but its not. my h3 sounds like a rich burner right now the sound only comes when i am in drive or reverse. someone told me that it might be the transmission and changing the fluid might help the sound. when i baught the h3 4 months ago the sound was not there only after i isntaled the intake..any help is greatly appericated thank you in advance ..

 

Well it is a Hummer!
There is a pump for the brakes that for some reason may be stuck on. Some people report hearing it run at shut down briefly.
With little details it would be a little less likely but could be the fan clutch is keeping the fan engaged?

 

Check your Vac lines. Where they attach to the intake and where they attach from the intake to the motor.

Also, the hummm might be coming from the air box itself. Sometimes aftermarket CAIs have a tendency to push or pull the OEM airbox into weird postions. Have a buddy put it in gear with you under the hood listening (make sure the ebrake is on and yoru buddy has his foot firmly on the brake!)

 

thank you i will try that. so can i rule out its not the transmission then?