[slikside]

Originally Posted by 67chevy_hotrod

It's not fan hittin radiator.. It definitely sounds like a transmission problem.. I will look into the rearend as well. I recently replaced the pinion seal.. It shifts fine and sounds fine at idle and at higher rpm. Under load or when I give it the gas a little aggresive is when it does it. This is irritating ha

Did the noise begin right then, or shortly thereafter? Always consider recent changes, especially when they "sound like" they could definitely be related to your problem.

I've never replaced a pinion seal myself, but I know that when it all goes back together you need a new crush sleeve, and it has to torqued just right...

I'm not saying it wasn't done right, just that it (or something related) could be the cause, since it was recently changed...