My toyota 4runner makes a squeeking sound when reversing. It only makes the sound if it's in reverse, but not when rolling back in neutral. What can it be?

sorry if it belongs in OT, since it's not s2000 related.

 

brake pads? wear sensors rub in reverse first

 

brake shoes could be draggin. check'em

 

thanks guys, I'll check into it. I think I might be the u joint.