Let us know what those suggestions were and how they worked out.
Interestingly, I don't seem to have the problems I once did with the rattle. One possible culprit I discovered some time ago: I recall repositioning the sub and noticed there was some play between one of the spikes and the spike "cup" (those discs that keep the spikes from marring the floor). It wasn't firmly seated. And I think this destablized the sub a bit at loud playback levels and caused it to teeter / vibrate. This would have exacerbated any vulnerable vibration points within the cabinet and/or plexiglass.
Anyway, I made the adjustment and things seems to be okay for the moment.
Regarding your sub's position relative to the carpet, what I first did was to use aftermarket spikes that had more clearance than those provided by Outlaw and were better able to pierce through to the subfloor. Later, I added a granite slab as a sub platform and that helped even more (view pictures 13 and 14 in my system pics album for a close up).
I think anyone who is using their LFM-1 on thick carpet should take a look at their ground-to-base clearance. It's pretty surprising how a thick carpet and pad can reduce the clearance compared to a hard surface.
I have to assume the proper distance between the bottom of the sub and the floor was based on a hard surface, not a thick layer of cloth.
McCormack DNA-125 (mains), Emotiva LPA-1 (surrounds)
Quad 11L (F&C) Wharfedale (R) LFM1 (Sub) w/ SMS-1
Squeezebox -> Behringer SRC2496 -> Musiland MD10 DAC
Sota Sapphire; Marantz 10B;
Video: Hitachi 42HDS52A; Oppo 971H System Pics