There is a service bulletin about the mounts for the AC pump, they're known to wear out and cause a 'knocking' sound. i think the fix was to put metal washers on the bolts but i honestly can't remember, i merely tightened the belt a little more and the sound went away (likely due to the tension holding the pump in place) haha.

V45W - 1999, 3.5 sohc, winter package
L042G- 1987, 2.6 carb, auto - Cylon Raider
A112 - 1973 Galant Wagon - 4G63 Turbo, 5 speed
L023G - 1983, 2.6 carb, 5 speed manual 4WD
L028 - 1983, 4D55 turbo diesel 2WD