Random thumping under floor boards..

[jmetz]

Hi so last night my truck started doing something it never has before..i was driving for about an hour before i parked it and it drove just fine, no rpm jumps or vibrations or shuddering etc..it shifted perfectly fine as well, but then when I put my truck in park it started randomly making a thumping, not steady just random intervals..can't hear nothing can only feel it in the floor boards, and I repeat it only does it in neutral or park, whenever it's in gear it perfectly fine, I drove it around a bit again after I first caught to it and it still shifted perfectly fine, I have good idea what it sounds and feels like when trans is going or convertor is shot, I also just did a transmission recalibration and got the oil changed one yr ago cuz it was doing the vibration and bit of rough shifting and stuff and that cleared right up..so anyway I read up on forums a bit and can't find anything super similar to what I'm experiencing so hopefully someone has some input? Thanks!

[jmetz]

FYI I just tried it again this morning and I cudnt get it to do it, drove forward a bit then I put into reverse to back up again and that triggered it, it made it bit of a slipping feeling then the thumping started faintly then when I put it into park it kept thumping..

[rav3]

What year, model, transmission & miles might help. Any mods? R u the original owner? Any maintenance done?

[jmetz]

It is a 2016 GMC Sierra 1500 Denali, 8 speed transmission, 217,000 km...no mods other then I recently put a different set of wheels on..but they are the stock 22" Denali wheels with 33" rubber..as well as regular maintenance yes

Edited December 9, 2024 by jmetz

[mikeyk101]

What about a broken motor mount(s)?

 

Maybe have someone in driver's seat with foot on brake and in gear. Slightly press the accelerator a few times and see if motor rises up some when doing that?

Edited December 9, 2024 by mikeyk101

[asilverblazer]

Serpentine belt?