subwoofer buzz - how to eliminate it

Check out Primacoustic Recoil Platforms. I have them under each of my three subs.They work best flat against the bottom in between the feet.Not expensive and they're returnable No more rattles and tightens the bass significantly.

@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.

@mijostyn I replaced the board in it and I probably need your tricks to make it tight. I may not have put it back together properly. 

hopefully you can fix the buzzing noise.  but you would definitely benefit from having a Auralex Sub-Dude-II isolation platform for the sub.  It isolates the sub from the floor.  great, inexpensive ($60) product that works.

@fred60 I am very inclined to try it, is it just a piece of foam with a piece of mdf on top? Do I need something between the sub and the platform, like springs?