Mechanics, shade tree ones included

[Cannonballkev]

I have a chevy K1500 with a 700 r4 tranny, open diff. 
  Here's the issue:  I have a weird sound coming from the drivetrain somewhere.  Its like a racheting,  rattling, creaking sound. Thàt is more present under load or when I hit the breaks, or when I shift from overdrive to drive.  Doesn't seem to do it in neutral.  Ujoints, rearend, axle, tranny?
I first noticed it the last time I left Bell mountain ( before they closed it). Maybe I tweaked something.
  Pulled boat to the lake today, really noticed it, not affecting performance, just sounds bad.
  Any suggestions?

[Big Dave]

I think you found it. You say when you shift or tow. I'd suspect  the transmission. Hard to diagnose over the net.

[Cannonballkev]

Ok, thanks. It's a weird sound that I've never heard before. And I've broke a lot of stuff over the years!