Zane;
I took another look at the noise in the time domain with a scope. I found that much to my embarrassment
the variable time base knob on the scope was not in the locked and calibrated position. I have not used the scope since I last looked at the file, so anything I said about a 60Hz component is probably BS. I have no problem falling on that sword, because I earned it.
The noise in general seems to consist of multiple grouped impulses of about 7 or so impulses per group. There seems to be a period of typically 25mSec between groups, suggesting an underlying group frequency of about 40Hz or thereabouts. This would definitely explain the "bassy" feel that has been expressed.
My old scope is getting crusty, and I really wish that I had access to a DSO, but that is not currently an option. Maybe looking at the file with an audio spectrum analyzer could reveal something.
At any rate, I struggle to think of how this noise ties a a common physical process. Most likely not power infrastructure, but what? DFing it with a portable might be the best bet.