There tend to be 2 forms of the SADS revolvers: Urethane and aluminum. (I'm not familiar with the urethane housings.) The OEM revolvers are aluminum. Inside the aluminum housings are the bushings. Through these bushings are mounting bolts that secure the SAD shaft to the revolvers, transferring the engine (crankshaft) rotational motion to the accessory drive in the front of the car. This provides for the operation of the alternator, power steering pump, A/C compressor, and radiator fan (I think - I'd have to check to make sure the fan is not electric).
It's the failure of these bushings that is causing the noise. The bushings no longer cushion the mounting bolts as the engine RPMs change (sudden changes like the A/C compressor cycling on/off).
Searched EBay and found:
Urethane
http://cgi.ebay.com/ebaymotors/ws/eB...category=33738
Aluminum
http://cgi.ebay.com/ebaymotors/ws/eB...category=33738
I have bought and installed the aluminum ones (but not from the seller in the link above - this seller wasn't around when I did mine). I got mine from:
http://cgi.ebay.com/ebaymotors/ws/eB...category=33738
buying just the revolvers with bushings and reusing my existing nuts/bolts/etc.
There are fairly detailed remove/replace instructions
http://autos.groups.yahoo.com/group/previa/files/
developed by folks on the Yahoo! Previa user's group
http://autos.groups.yahoo.com/group/previa/messages.
You'll have to decide for yourself if you can manage the remove/replace. It may be that you can buy the revolvers and provide them to your mechanic for them to install. I'd check with them before I bought though to make sure.
Wm
92LE