Dude, sounds like a botched job.(not trying to put down your friend) When I was attempting to do this I was defeated by the lack of a press. 3 times, I left the garage with no sounds thinking all was well, each time the whining came back instantly. Upon investigation, the pinion bearing was loose, the race had settled and pinion gear moved away from the ring gear.

Anyway, I might be bearing bad news. After driving only a few miles like this, I went to a shop to have it set up by pros. They could not get the gears quiet for anything. They had worn weird and have whined ever since. You might be stuck with a whining diff as well, maybe not. Either way, I'd stop driving it and bring the thirds in for investigation.

Frank.