fd rotar tt

hey i recently put a new engine in my car, i had some turbo problems... but now im going single... but anyways i know this is really hard to diagnose by not hearing it but i have a weird almost whistleing type of hum cominging from the back of the engine possibly trans area but i cant really tell... i doesnt sound like it get louder when i bring the rpms up. but when the engine is slowing down when i shut it off the sound slows down with the engine until it stops spinning. any ideas? like does anyone know what bearing failure in the engine sounds like? the car runs good other wise doesnt really smoke burns pretty clean for not having any emissions, and by the feel of the engine it seems like it has really good compression. please help