We have a rather high noise level around here on 160 thru 40 (I use an
MFJ-1026 to cut down on the noise and it works pretty well ... but, I
digress...).

During rainy weather, though, the noise level seems to go way down, from
S7+ down to S1 or S2.

Reading everything I've read about "precipitation static" and such, I
would have expected it to be the other way around.

What is it about general "noise" that makes it go way down during rainy
weather?

Antenna is a 160-meter inverted V up 50+ feet in the center and fed with
ladder line, but I see the same effect on my 17-foot-high coax-fed dipole
for 75 and 40 meters.

Noise goes down so low that I'm thinking about setting up a sprinkler to
keep the antenna wet! :-)