This has been bugging me for awhile and I figured I'd finally ask.

Everytime I come to a stop and have to wait there for a red light or after I shut it off I start hearing a thumping sound coming from the passenger side of the engine compartment. It lasts maybe 10 seconds then it goes away. Very noticeable when I park the truck since it starts when I stop and continues for a few seconds after I shut it down. I'm never fast enough to pop the hood to look and listen where exactly it's coming from.

Does not matter if the truck is cold or warm and there are no other consistent factors.

Anyone else ever have this problem or no what the deal is here?

Thanks.

 

HVAC Vacuum reservoir, or its check valve?

After shut off, move the heater/ac selector and listen. If the reservoir/check valve is good, you should get several actuations (doors moving) that you can hear.

If you hear no movement (you can open the glovebox all the way to hear it better - press the tabs in) I'd suspect you aren't trapping vacuum because the check valve is bad, reservoir is cracked or the vacuum line is cracked/loose.

Try to rule this out by keeping the heater/ac in OFF.

 

Thanks, I'm going to have to check this out.