Update: Finely pulled the regulator out to see what was making the popping sound at full close; it was the drive gear slipping on the cable. Both looked to be worn! Nothing was wrong with the part that attached to the window glass frame. So the part that some said I needed and I ordered off Ebay was not the problem.
So I bought a new complete regulator with motor from AutoZone for $119 and it comes with a lifetime warranty so if it ever fails again, no cost to me….
Bought one of those Bondo Dent Puller Suction cups to hold the window glass up while the regulator was out, worked like a champ.
Took me about 30 minutes to replace the left rear regulator, not a bad job.

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Supporting Vendor and Moderator of LOST05 Jeep Liberty CRD Limited 
Ironman Springs/Bilstein/Shocks
Yeti StgIV Hot Tune
Week's BatteryTray
No FCV/EGR
Samcos/ProVent
SunCoast/Transgo
Carter Intank-pmp
2mic.Sec.Fuel Filter
Flowmaster/NO CAT
V6Airbox/noVH
GM11 Bld.fan/HDClutch
IronrockArms/wwdieselMount98 Dodge Cummins 24 Valve