subwoofer buzz - how to eliminate it

@grislybutter , I have been building subwoofers for 40 years and I am the master of buzz/rattle elimination. 

First is to make sure the buzz is coming from the woofer. The worst buzz I ever had turned out to be coming from my theater screen but darn if it did not sound like it was coming from the sub. Get rid of any extraneous parts like grill cloth frames. Mount the sub on three spikes not four! Make sure the driver's screws are tight. Most drivers are mounted on a gasket. I mount mine on silicone caulking. I think it works better. You can still get the driver out but it will be a little more difficult. I use a trim tool (automotive) to pry them up. Lastly is check the driver. Dust caps are frequent offenders. It can be hard to determine but if you tap the dust cap lightly you should hear a thud not a click. If it is suspect run some thin cyanoacrylate glue around the edge of the cap. It will run under by capillary action. Just a little! you do not want to glue your voice coil in place. Next is gently push on the cone with your fingers surrounding the dust cap to push it back and forth. If you hear or feel any grinding noise the driver is bad and you will need a new one.

You do not want to isolate the sub from the floor. You want to do exactly the opposite which is fix the sub to the floor. This is what spikes are for. Use three, two up front and one in the rear. Trying to isolate a sub from the floor is folly. Bass waves are very powerful. If you have a bad floor that resonates it will do so even if the sub is mounted on the ceiling. If the floor is that bad the system need to go in a room with a sturdy floor. Spiking the sub to the floor keeps it from shaking so much. Any shaking or vibrating is distortion.