About six months ago we hired someone to fix the squeak in our dryer, a
Frigidaire FDE7977ESO. They replaced front glides, rear bearing, and
lower felt.

Now a squeak has returned, only it's much, much, much louder. It's
ear-splitting. When it's squeaking I can' t be in the same room without
ear plugs. It seems to be coming from the rear of the drum.

Could the rear bearing be shot already, in six months? Is there
anything else I should check?

The noise occurs once per revolution of the drum.