peter p

I have a 2003 f150 super crew 4x4 and every time I hook my trailer and tow about 600 lbs, I get this squeaking sound (sounds like see saw see saw). It sounds like it's coming from the rear u joint area (the u joint seems ok).
It does it real loud when accelerating lightly from a stop and then quiets down the faster you go. It only does it on acceleration and in "Drive". If I put it in neutral and accelerate while driving it does not do it.
It's driving me crazy because as soon as I unhook the trailer it won't do it or does it but not as loud.
Does anyone know what it might be?

Kattumaram

The conditions/noise seems to be consistent with a dry U-joint. Accelerating under load causes the rear axle to wrap around the springs increasing the drive angle of the rear U-joint that would exacerbate any condition that would cause noise.....but, just a guess on my part, so don't discount my opinion if the cause of the trouble turns out to be something else.

peter p

Yup, it was the u joint.
I removed the rear one where the noise seemed to be coming from and one end of the joints needle bearings were rusted out and destroyed.
I replaced both u joints and everything is good.