So today I took a 300+ mile round trip drive with my truck and along the way it developed one hell of a humming noise coming from the driveline.
It seems to be worse at slower speeds and when slowing down or accelerating. Its consistent at speed. Driveability isnt affected at all, I was still able to drive 80+ mph without an issue.

A few weeks ago I got my tires rotated and after that I noticed a slight hum when slowing down to a stop but I thought it had something to do with the tires because I hadnt gotten them rotated in quite a while. Apparently thats related to the current issue and its gotten worse.

What could possibly be the cause?

'06 XLT Supercab, 5.4, 9.75" limited slip rear, 4x4