most likely the 3 plastic bushings in the motor need to be replaced. They are designed to be eaten up to give some slack in the motor and over time result in sticky 1/4 windows and that popping sound. You can buy the replacement plastic nubs in the help section of Autozone for like 7 bucks or IMO if you want a better solution simply use 3 quarter x 20 nuts..
They are very easy to replace. Remove the rear lower seat, remove the rear inner panel enough to reveal the motor. The window motor is attached with 3 bolts. Then unplug the wire. You'll then disassemble the motor and clean out all of the old plastic bits and grease. The new nubs go on with the radiused side down and they can be a little tricky to get them all go in flat. you sometimes need to tap the cover back on with a hammer. If you instead use the nuts they will fit right in. Either way also pack the motor with some grease and put grease on the gear and lubricate the bushings and sliding tracks with some white grease.