Help diagnose my engine sound.

[KJDevildog]

Hey everyone! Just trying to diagnose a sound that is coming from the engine of my 06 KJ.

When at idle with the brakes applied, or when just rolling to a slow start from a stop I can hear a thumping sounds from the engine bay. It gets slightly louder under acceleration, and transfers from a thump sound to a thap sound. Once driving at a normal speed I don't hear or feel it anymore. Also, I can feel it just barely in the gas pedal. Though when under the hood and manipulating the throttle by hand, I cannot hear it.

Also, it does seem to be a lot more audible with the A/C on, which my wife wont drive without.:freak3:

 

[ridenby]

Maybe have a look at belt tensioner,it has some marks to show slack.

 

[BjBnet]

that belt tensioner is a nasty little bugger. Funny the different sounds it can make. Mine was making a whining noise and did it while accelerating and shifting, had me thinking my steering rack was shot or maybe the steering pump...at least until I popped the hood and I could hear the pulley making noise.
Picked up a Dayco assembly this week and changed it (took about 20mins) now it's nice and quiet.