@psychictides

The first thing I would try is muting the #MasterBus, leaving all the other settings the same, rendering a silent version of the same track, uploading it, and checking if the hum persists. If so, then the problem is probably somewhere in your #rendering chain, and you can start making minor tweaks, one at a time, to find the culprit by process of elimination. Some examples of minor tweaks I'd try:
- the #SampleRate and #BitDepth (e.g. 48/24)
- the #dithering settings (e.g. on/off, type/style, etc.)
- the file type (e.g. #WAV, #AIFF, #FLAC, #ALAC)

I hope that helps, but if it doesn't, you should probably reach out to #Bandcamp support.