5th gear vibrations

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83 RX-7 Gsl, 2000 Mazda Protege LX, 2011 Mazda3 Sport i
Occasionally my p5 will start to vibrate the shifter to the point where I can't help but hold the knob so I can have a conversation. I just recently put in a mx-3 short shifter that I swear can't be the issue. Maybe engine mount? Lemmie know your suggestions!
 
The first aftermarket shifter I installed in my 01 Corvette did not include the vibration-dampening material that was in the OEM shifter. At certain RPMs the shifter would vibrate quite a bit. Later I swapped it out for a C6 Z06 shifter and that solved the problem.

I suggest you swap in the OEM shifter. If the vibration and resulting noise go away, you know what the source of the problem is.
 
My Karboy shifter rattles really bad in my MSP, even with the knob off. I am planning to reinstall the stock shifter.
 
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