Like freeway on-ramps or around tight curves under acceleration. The sound is very high pitched - like a dry bearing might sound. Goes completely away when driving straight and not really noticeable when making normal turns. There needs to be some pretty hard centrifugal force applied before I notice it.

I have stock tire size, so it isn't tire rubbing. If I had to guess, I would say it's coming from the rear. I have about 53k on the truck. Could this be the rear brake linings dragging, wheel bearings, u-joints? Any suggestions how to diagnose?

 

I guess I would start by jacking up each wheel (safely) and see how they feel when you rotate them, and/or use a bar to see if there is any slop.

You might also look the truck over generally. Motor mounts and stuff...

 

Are you sure its not tire squeal, have you backed up over any curbs, if the rear is not square to the truck it can cause that.
Hard for a rear wheel bearing to go dry, have you checked gear oil level?

 

All good suggestions. Doesn't sound like tire squeal - but I guess anything's possible. Gear oil is due for changing and I was thinking of adding an aftermarket differential cover. Probably time to do that.

 

Do check the engine mounts. I've seen other vehicles where a bad engine or transmission mount resulted in a belt or pulley hitting a shroud when cornering and accelerating.