I get a sense you are handy with electrical repairs. You could "jump" (bypass) the switch at the connector with 2 jumper wires, then turn on the key and see if the window goes down (or up). Turn off the key when it reaches the end of the travel to avoid tripping the circuit breaker. If you get the same chattering noise, the regulator is likely at fault, or the window is binding and the guides should be lubricated.

If you would like a scan of the '98 V70 power window schematic, send a message to n0v8or@cox.net. I'll reply with the scan attached as a jpg image.

If you need some guidance regarding which terminals to jump, let me know.