It's developed a rough whirring(?whining, but harsh) sound from 2500 rpm and gets louder/harsher with higher rpm. Does not need power to cause that eg same with engine braking but maybe not quite as loud, but only just. Not the engine, when revved in neutral no sound.

Anyway, I can't seem to determine what transmission it has ie the exact model. Any ideas?

[Thanks Blakamin, now title edited]