Loud bang randomly 03 v8

[Moist]

It's coming from right next to the transmission, just aft of the engine where the two mate. It feels like something kicks the floor rather hard.

It consistently happens immediately after the car stops, and sometimes about 30 seconds after the engine stops. It does happen intermittently while driving, but it is usually drowned out by the cacophony of other noises.
It is accompanied by a misfire on occasion, but this is only during startup. (90% sure I need new plugs)

I thought it might be the exhaust, but I can't get the play required to force it to make the sound/impact something.

I'm not sure what causes it, and have been chasing it for about two or three months. I really don't know what could be moving that much when the car is off to do that. Any ideas?

(EDIT: I'll get a video of it later.)

 

[AuSeeker]

It's coming from right next to the transmission, just aft of the engine where the two mate. It feels like something kicks the floor rather hard.

It consistently happens immediately after the car stops, and sometimes about 30 seconds after the engine stops. It does happen intermittently while driving, but it is usually drowned out by the cacophony of other noises.
It is accompanied by a misfire on occasion, but this is only during startup. (90% sure I need new plugs)

I thought it might be the exhaust, but I can't get the play required to force it to make the sound/impact something.

I'm not sure what causes it, and have been chasing it for about two or three months. I really don't know what could be moving that much when the car is off to do that. Any ideas?

(EDIT: I'll get a video of it later.)

Do you not think it could be the slip joint on the drive shaft, it's known to clunk when stopping when it needs greasing, try greasing the Zerk fitting on the slip joint until you see slight movement this usually solves the problem.

 

[ArthurKotb]

I would agree except I've never had it happen while driving. I experience a "bump" sometimes when stopped at a light. It happens whether I just greased the slip joint or whether it's time to grease it again. (I don't put as much grease in there and that seems to have stopped the bump. Like AuSeeker says, add grease until the shaft moves.) The other time is when I back out of my driveway (maybe 25') stop and put it in D. I let it roll forward and I get a little bump most times, especially first time each day. It doesn't do it anywhere else so maybe being parked on a sharp rise like my driveway has something to do with it.

I wouldn't classify either of those as being a "kick", just a slight bump. Still, I agree with the slip joint. Have you greased it at oil changes along with the U-Joints?