Your probably letting your transmission roll forward or backwards after you put it into park. This puts pressure on the transmission where it stops and it "pops" out of park for this reason, making the loud noise. Apply the E-Brake after putting it into park but before you let off the regular break, it wontcontinue to roll.
check engine mounts
Worn out bushing or steering joint probably.
check the fluid in the rear end it might be dry causing medal to grind causing a clunk noise or the gears in the rear end or worn done causing it to do the same thing
They grind their teeth and it makes a chattering sound.
If it's a clunk sound, check universal joint bearings and drive shaft bolts. Otherwise please describe noise.
a clunk noise over bumps
One clunk when accelerating (but now repeated clunks) and another when braking can be caused by broken motor mounts.
I'm going to assume its an automatic transmission. Is the millage higher than 50,000? If so try changing the transmission fluid.
They could squeak, rattle, bang , clunk.....
You have either run something over or your car is due for a service
most probably the noise is from the pipe expanding.
You need to use the clutch and the shifter smoothly together!