Hi all, this is my first post and I wish it was for other reasons. I have an '05 2500HD that I bought used three years ago when it had 48000 miles. At roughly 55000 it started popping loudly during acceleration and set a code. The vane position senser was replaced and the problem was solved. About eight months ago the turbo was replaced at 64000 miles, and has run fine since. Until yesterday. I took a short road trip (about 240 miles round trip) pulling a small 5x10 landscape trailer (unloaded) and the truck ran fine on the way. Coming home, I stopped for a bite to eat and left the truck idling for about 15 minutes while I ate to keep the A/C going. When I got going again, I heard a very strange, loud noise at lower speeds under moderate acceleration. Very hard to explain, but kind of like a squawking or a rapid bleeding off of pressure. Once on the highway, I noticed it would also make the noise when would let off the throttle after makng a pass, or just after the truck would upshift after making a pass. I have no check engine light on, engine temp was around 200, trans temp 200, oil pressure is fine. It did seem a little down on power while this problem occurred. I tried to duplicate the issue last night and couldn't get it to do a thing. I'm due to take this truck on vacation in two weeks, and fear the dealer will tell me they can't find anything wrong. Any suggestions? Thanks, Rich

Also, no mods to this truck except for exhaust.

sounds like the cooling fan was engaged since you let it idle for about 15min with the a/c on. when it engages its a very loud sound. another reason why it sounds like its hte cooling fan engaging is bc when you tryed to duplicate it last night, the cooling fan didnt engage becuase the engine was cool enough where it didnt need it.

look at all the turbo inercooler boots and make sure they are not loose or poped off.