Driver's window pop pop pop
 

Yesterday, my drivers side window started making a faint pop pop pop sound when it is going down the last 3/4. it doesn't make this sound going up. Any ideas?

my window starting doing that not too long ago. Took the door panel off and noticed one of the rivets holding the window motor in was really loose.

^^^ That's what it is. Most likely loose nuts and bolts that someone used to replace the original motor with.