When I enter AUX mode on my stereo, a buzzing/humming persists.

[Fazalian]

This happens even if there is is no AUX cable in the AUX port. Simply selecting AUX mode causes the humming. The Stereo I have is a Panasonic SC-PMX70B with 2 speakers. The humming comes out of both speakers. The stereo is not connected to any additional devices. Can this be fixed?

 

[ex_bubblehead]

Hum is from 50/60Hz mains leaking into an ungrounded or poorly grounded audio section. Yes, in the majority of cases it can be fixed by finding the bad ground and tightening it up, either via tightening a screw/nut or resoldering a cracked solder joint (often more than one). You will need schematics. Alternatively take it to a repair shop.