When the engine mounts go bad, it can induce a clunking sound whenever you're accelerating.  There are two of them that secure the engine, one on each side.  Each engine mount is compromised of the rubber engine mount itself and a metal protective top cover to shield the rubber engine mount from heat and oil / grease that may drip onto the rubber engine mount itself.  Replacment engine mounts only replace the rubber engine mount itself, so you need to keep the metal cover.  The rubber engine mount consists of a center rubber center core sandwiched by metal plates with threaded studs attached.  It's the threaded studs that secure the engine mount to the engine and engine cradle, and the rubber center core handles the compression and tension forces from the engine rocking back and forth.

Mazdaformance offers Mazda Competition engine mounts for an upgrade.  These upgrade engine mounts are stiffer than the stock OEM Mazda units.
Mazda part number:  FBY1-39-040

Questions?  Comments?  Send mail to:  reted@fc3spro.com