Had a friend riding with me and he asked, what's that thumping noise? Can't say I have heard it before but now that he has pointed it out to me it's driving me crazy. Approximately every 20-25 seconds it sounds like something bumps against the bottom on the passenger side floorboard. I got out and from the outside I can't hear it. Can only hear it on the inside cab. Doesn't matter if I'm going down the road or sitting still, every 20 or so seconds...thump. The truck is stock. Any ideas what I might be hearing? Doesn't seem to be adversely affecting anything that I can tell atm.

Its likely one of the doors for the heating and a/c cycling like mine does . There was a update to stop that but when I asked the dealer to do the update apperently they forgot . Wonders if I took it in seening its out of warrenty if they would reprogram it and bill me .

Ya i have that same thumping noise when im sitting and idleing and the heats on. If anyone knows the calibration number or what the bulletin number is it would be of some help. You know just so i don't go into the dealer and they look at me funny.
thanks

i have it also. Here it every once in a while usually when the front defroster is on.

If it happens with defrost on its the A/C compressor.

Yep it is the compressor comming on to de humidify the cabin air. It cycles on the low pessure switch alot due to out door temp.

Thanks everyone for their response. I do greatly appreciate it.