It could be something to do with the servo / amp for the heating. Is that system working OK? You could pull that fuse to confirm.
Does it sound like it could be a relay buzzing? All this stuff is in that area.
The heating seems to working OK.
Checking the fuse panel guide I can't seem to identify a fuse for the servo/heating amp. What it be under another name?
I have ruled out wildlife being the cause of "the noise".
I have observed that the auxilliary fan (AF) is constantly going from the time the car is started. The AF will run at different rates when "the noise" is occuring. When "the noise" is absent, the AF runs at a constant speed. I removed the fuse for the AF and "the noise" continued on. (I did this not knowing if relays are before or after fuse panels.)
I have observed that the interior light located below the glove box will flicker when "the noise" is occuring. When "the noise" is not occuring the light stays at a constant brightness.
"The noise" appears to be very close to the fuse panel.
Yesterday I drove the vehicle 50 miles and it ran fine except for "the noise".
Any suggestions as what to do next except for turning p the radio?