thumping sound coming from engine bay when at a stop

wells i researched a little bit a found out a little bit but wanted your guys opinion..

this is for a 2002 double cab 4x4 by the way, no locking rear diff if that makes a difference...

when truck is in park or neutral, there is very very very small thumping sound coming from what sounds like the passenger side firewall inside the engine bay. (sounds like when you turn a bucket upside down and tap on it)

when you put a load on it ex: reverse or drive, the thumping sound gets louder.

then if you turn the a/c on while in reverse or drive the thumping sound gets even louder...not super loud, but you can notice that it does get a little bit louder.

i've search and one thread came up with the same problem and they told him/her to lube the drive shafts and components and to also check the rear brakes for some kind of leak? don't know how that has anything to do with the thump but i guess...

and i don't think that this is the infamous axle wrap thump that keeps popping up when i search, this thumping sound goes with the idle of the car, like if i listen carefully the thumping noise well thump faster when i rev up, and thump slow at idle.

so any input guys? it's really starting to bug me....

thanks in advance

 

Loose exhaust some where some how. It's making contact somewhere.

 

Check the condition of your fan belts and pulleys. Sounds like you are looking for something related to engine RPMs,

 

yea...i just bought the truck used also, and it doesn't look like they have changed the belts...

 

Did you ever come up with anything?

 

Flywheel maybe? Sounds like there's a few threads on this sort of noise recently.

 

To the OP. Any updates? Have you changed your timing belt or te idler pulleys?