Weird sound coming from back

So I have about 170k on my beloved, recently there has been a repetitive screeching sounds coming from what seems to be the rear.

Symptoms:

1) metallic screeching noise
2) not constant, rhythmic about every 1 to 1.5 seconds .
3) only noticeable above 45 mph
4) all brakes relatively new less than 10k miles

Ideas ? Please don't say bearings !!

 

Wheel bearings usually sound more like a hum at higher speeds when they're going out.
Might need to pull the wheels and see if everything looks good. Maybe something caught in or around that area?

 

Put it up on jackstands in the rear and tap the throttle or push it in neutral to see if you can recreate the sound...?

 

As an update, I got the truck on some stands, the rear brake adjuster was somehow wayyyy over tightened, causing the rear shoes to butt up against the drums. Quick adjustment of the adjuster mechanism, she is all good now. Thanks for the advice TW!!