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!