Okay, I've been a member here for a while and I've not seen anyone mention this, so either I wasn't paying attention or no one else has this problem.

I read about these drivetrain "clunk" sounds all the time here at F150online... the only sound my truck ever makes is under a spirited launch from a stop (not full throttle) or under decently strong braking.

After a while, I determined that it is actually the driver's seat sliding an almost undetectable amount forward when I brake and toward the rear of the truck when I accelerate. Initially I thought it was driveshaft slop, but I know it's the seat. The truck can be stationary, but if I grab the steering wheel and pull forward or push back I can get the seat to move just a little.

Anyone else ever notice this?

 

my fiance's truck did that... the seat wasn't fully bolted down to the floor pan.. the bolts just needed tightening. it only happend upon sudden breaking