What is this stupid sound?

Alright so I jacked my wheel up, spun it forward and back and didn't hear anything, I tried the shaking it side to side thing and didn't see or feel any unwarrented play ( maybe a fraction of a fraction of a inch) but it's a frankenstien truck. Anyway I took off the wheel and checked the brakes which seemed fine but there was a biggish rock between the dustpan and the rotor so I figured hey maybe it was that. drove it around and made it around 20 miles before BAM! It did it again... The sound randomly happened, doesn't sound like a rumbling, it sounds like... sort of like when you get a belt changed and don't adjust the pully - like a high pitched squeeling. when it happened I could feel a little resistence on the left front wheel as if the brake was on a little bit. but no wheel wobble that I could feel and no rumbling or anything. I slowed down from the 40 mph that I was doing and turned off the road and made sure my hub wasn't locked or something (never know what the kids may do) I wasn't and so I obviously had to still drive home. It didn't really make the sound again besides a little more of the squeeking. 

Any ideas guys?

Thanks!

Wheel bearing/worn hub.  i.e. spun bearing.

Hey CR,

I had this same type noise after putting new front brakes on the beast.  It was the hub grease seals.  The outer seal was a fraction too tall and would squeal on the spindle face.   I had to slice about a mm. off the edge of the seal, and the noise was gone.

Good Luck.