One of the suggestions never occurred to me, which was to check that the binding posts were not loose. That was not the case but it never crossed my mind to check something so obvious.
The other was to unscrew the amplifier section and look for anything loose inside. I never got that far because, after accidentally bumping the cabinet with my knee in the process, I noticed that one of the vent ports was the cause of the vibration.
The Outlaws provided me some directions on how to apply adhesive but also offered to do the work for me. I am not the handiest person, so I opted to ship the sub for repair.

Thanks garcia:

I will check my ports next time I play the sub loud.

I have noticed distortion coming from that area before. I thought it was either the driver over-extending itself or excessive port chuffing. I will focus on the port vents next time.

BTW, there is one demo that makes the LFM-1 go plum crazy in this regard, it's the 4th track from Kraftwerk's "Aerodynamik." Though I doubt you or the Outlaw team own it, I would love to know if it causes problems with other LFM-1s.

Very odd, considering it can handle bass tracks like U571 with relative ease.

Best,

- Jim