Rocking C20 with my finger prior to re-solder I found the noise dropped in and out. (be careful when poking around the N72 while it's plugged in)
A quick re-solder and the noise went away.
Good Luck on your troubleshoots,
-A
P.S. C20 cap sits behind the bournes pot. My hunch is the cause of my problem was when I went to mount the front plate, some of the pots did not fit perfectly in the holes and tipped back on their solder joints. The back of the pot then pushed on C20 and broke its solder joint or otherwise damaged the lead going into it.