no there isnt a scraping noise...and the thing is ive just heard it's called powershifting when you downshift an automatic..im wrong about that...i was seriously only going about 30...wasnt revving up the engine or anything...just shifting down is all..i just wanted to coast in second cause it was on a a back road...i dont think doing that damaged anything..my friend has a heavily modded mustang and it's an automatic...he HAS to drive it like manual because the transmission slips when he has it in regular drive...like he'll start out in 1st gear then shift to second then drive..it's kinda funny really but yea he does it all the time and it hasnt done anything to his engine that i know of

 

For your buddy in the stang, if the tranny is slipping when it shifts normally, then its slipping even more when he's manually shifting it, its just the rpms are higher so it "feels" like its slipping less, putting even more heat in the tranny, it won't last My guess is he feels cool by shifting it this way since he drives a stang

 

I had this same issue several times with several different Models of chevy. One was on a 99 Cavalier, when we were syphoning the gas out so we could replace the fuel pump, we noticed some sludge in the tank, and the same sludge in the filter. Replace them both and cleaned the tank. Ran fine after that. Also have a 95 firebird, for it, I had a friend replace the waterpump for me, and when he did, he forgot to plug the coil pack back on it, so check your coil pack too.