Just purchased a 2007 Hummer H3, first GM vehicle I've owned. I've been having multiple issues and taking them one at a time. Currently, there is a periodic (every 20 to 30 seconds) flushing noise behind the passenger side dash. Happens when I turn the heater on. I've been doing some research and the closest solution I can find possibly the evaporator expansion valve from this post.

Any suggestions would be greatly appreciated.

 

Could be the on board toilet... if yours came with the adventure package that is

 

Had 2 S10 chevy extremes one was 2003 the other was 2000 the newer one made the sound and the other DID NOT also the windshield on the one with the sound fogged up quite often on initial startup. I returned it after a 2 yr lease then purchased a better older model same truck (but stick shift.) I had a few warranty issues with it mentioned the sound and fogging issue while booked in for winshield wiper motor replacement. Never got fixed. Sorry can't help you other than to tell you had similar issue. I always thought it was air-loc in the heater core or lines?

 

I've had those sounds in vehicles too. As someone mentioned, I always assumed it was the heater core and I would end up replacing it soon. I've only done one heater core in a late model car and it is a b@%#^. I helped a buddy do his Mustang and we had to take the whole dash out to get to it. On the cars that I had that did it, I just lived with it. Figured if I ended up with water in the front floorboard, then I would fix it. Never had to.

 

Actually i recently had a radiator changed out.. and maybe heard this flushing sound acouple times... i think its eather water being put back in reservua or it could be air in the radiator hoses thus a swooshing noise upon circulation would ocur.. think ill open my cap today and squeeze a hose and reseal hoping to air tight it.. but i put my money on the reservia tank maybe... i dunno.

 

I have the same sound but it needs to be at least on click into the defrost settings. From a long time ago, I thought someone had said that was the canister purging itself but my memory isnt't what it used to be so I could be wrong. I don't think its a problem as mine has done it from day 1 but I understand how it could be annoying.

 

All,

Thanks for the advice. I did get the radiator replaced recently, so I'll give it some time to cycle through before I rip off the entire dash.

Again, thanks!