Sounds like the gearbox for the wiper.  May need a new one.

Search this newsgroup.  There is a post for disassembling the wiper and
greasing it.  It will work wonders.

When this happened to me it turned out to be a bushing that was shot
in the assembly on the drivers side (motor was fine). I suspect it may
have been loosened when the W/W stuck to the windshield a few times
during an ice storm. Once loose, the wear took it's toll.

I ordered a replacement from a junker at Potomac German Auto Parts
near Baltimore, I lubricated it, installed it and It was still fine
when I sold the car four years later.