This particular outlet was switched, and whenever I would flip the switch to ON I would hear a humming for a few seconds and then the circuit breaker would pop. The seller told me the tenant had a CNC router or something of that nature plugged into the outlet and apparently that worked without tripping the breaker. I have no idea, maybe the dude wired up the polarity wrong or something. I deleted the whole outlet (along with the wall it was in) and the rest of the outlets and lights on the circuit are working normally, so I'll never know what the exact problem was.