Maybe a vacuum leak?
 

I've been noticing a sound (not very loud) that seems to be comming from the interior on the passenger side somewhere under the dash maybe. Kinda sounds like a pressure relief valve letting go. Lasts about 2 or 3 seconds. It's under low throttle when the vacuum would be high. Any ideas?

Had the same problem. Turned out my wife hit the vacuume line with her foot and disconnected it. Look up under the dash by the firewall, and you'll see it in plain view. Just plug it back in.:D

I looked near the passenger foot area a couldn't see a thing. No wires hoses or anything (might be different on an Alpha). Any other ideas? Definitely comming from that area. Maybe under the dash or the kick panel?

stinger95....my sincerest apologies! It wasn't my H3, it was my wife's Malibu and I was the one who knocked the hose off.:o They say your mind is the second thing to go as you get older. Anyhooow....it could still be the same problem on the H3, only, the vacuum hose could be buried up under the dash somewhere because it still uses a vacuum system to activate the HVAC air doors.

definitely sounds like a vacuum line

Does it only happen when your A/C is running? If so, it's likely your evaporator expansion valve that's causing the noise.

I can't remember but there may be a GM Service Bulletin out on the subject.

I think you should consult with mechanic, the possibility of other thing, can be happen.

It may be your air pump clogged or one of the tubings near the air pump. The H3 comes with a closed air intake system, which is a good thing when you're offroading. But it can get clogged damaged.
The Air pump is located below the air intake. There is a hose coming from the air intake to the air pump.

Thank you for addressing an issue from a THREE YEAR OLD THREAD! :rolleyes:

Please check the vintage before you post.
https://www.hummerforums.com/forum/n...bumping-23220/