[AZKen]

You need to see if there are splined posts coming up thru cowl and see if they move. Put your hand on the wiper motor and around and see if you can sense what is rumbling. Could be a loose wiper motor mount. There is a rocker bar that reciprocates back and forth on motor. Are there any transmission arms from that bar going to each wiper post? Take it out. Could be broken gears, may be only nylon.
Did you see me say someone has a switch and knob for you? and a motor if you want it. Fairly near you. Very reasonable indeed. I asked you to PM me.