01 Silverado - interior fan speed surges (with a/c on or off)

[jocko]

Mostly notable at the high (#5) setting, probably just because I can hear it better, but it also happens at lower fan speeds.

Probably not too uncommon, so before I dig into it (am assuming blower motor - don't think I have any clogs..?) was wondering if anyone had any intel.

Thanks in advance for your tips.

Btw, probably will do multi things at once when I fix this - my a/c doesn't blow as cold anymore, needs to be recharged (it's an '01 and never has been charged, although it is at least cool still). I live in the desert, has been in the 1teens for over a month now, I need to get the system back into shape.