In the end of the ROTJ, when Vader throws emperor down and the blue shit pours up from the shaft, we can hear three man voiced moans that mumble something unrecognisable.
It sounds like: "WHY? WHy? Why? why?..."
The moaning begins about 16 seconds after Vader gets his change of heart and picks the Palpy up.
ADDENDUM> On further study, it seems that the moan heared during that period is not the choir to the "Emperor's Theme", but perhaps it is Palpatine himself, before his sould is truly destroyed.
Btw... The music in that scene is responsible for about 100% of the atmosphere and emotional content.
Just thought how ridiculous it must have been "on the spot" with no music and stuff.
Imagine.
Old man is zapping a young boy with his lightning attack while a man in mechanical suit stands next to him. He then suddenly picks up the old guy and tosses him into a shaft nearby! Its comedy.
Just watch the scene with no sound and it makes Vader look like a total idiot. Just standing there until finally being able to make the gorilla-style assault.