Another "What's that horrible noise" question...

[mwb9520]

Hi All - My first post and looking for input and opinions before putting the truck up on the lift this Wednesday.

1972 GMC Sierra, 1/2 ton, 2wd, LWB, recent crate motor and rebuilt Turbo 350, also new brakes front and rear.

No engine or trans noise at startup or idle. Nothing really noticeable driving at low speeds through the neighborhood at 0 to 35 MPH, but once accelerating up towards 40 I can begin to hear something like maybe a U-joint chirp, but noise doesn't increase much while under load all the way up to 50 MPH...but as soon as I let off the throttle it's like WTH IS THAT? Very loud grinding sound, but goes away again under load and at low speeds.

After reading some of the other posts on here, I was planning to R&R the U-joints and inspect the carrier bearing this week, but also wanted to know if there is possibly anything else I should look at while I'm under there...Thanks, Mick