thought it was the dual mass flywheel starting to let loose on me but i have this high pitched pulsating drone that is always present at idle. i was under the truck listening the other day, even busted out the mechanics stethoscope and i swear its coming from the exhaust. sounds loud in the cat, could it be getting clogged up? can't hear it once im driving just at idle.

 

Did you check the rubber insulators on the hangers? One of mine vibrates like crazy between the metal hangers which creates an embarrassing and annoying drone at idle. With the truck idling in Park, crawl under and touch each hanger and see if one of them is the problem.

A couple days ago I finally wrapped the wiggle room on the hanger with some tape to hold that rubber in place. Now the truck is quiet at idle.