Sounds like the rear bearing gone bad.
The bearing is not available separately and it comes as a part of the rear outer tub assembly.
It is a pretty serious job and your decision should be based on your experience and condition of the washer.
- The part number for the rear outer tub assembly is
AP2578105
Here are the break down diagrams for the Frigidaire washer
Model FWTR647GHS0
Gene.