weird brake noise

I am helping a buddy out by doing his brakes tonight on his 96 xj. The passenger side is making a houling noise from the passenger side when i accelerated from 30'ish to 50'ish. other than that it is silent, and it didn't change with brakes, it stopped when I let off the gas, or didn't accelerate as fast. I have never driven this one before. I have done the brakes on my own countless times. I took off each wheel again and checked the caliper bolts. they were plenty tight. I replaced all the pads and both rotors.

could this be caused by a bad caliper?

it could be a hub going bad. If you want to check it jack up the heep so the tire is off the ground and see if there is any play. Grab it on the bottom and see if it moves toward the engine in and out