I purchased mine on ebay and installed myself
The diff. side mounts are around $150/ea. for the part only. You can buy just the bushing if you have access to a press for only $20/ea.
https://www.ebay.com/p/Mazda-L2142868XB/1857687836?iid=252607652251&rt=nc&opts=opick&thm=1000...
My wife's 2007 CX9 GT was exhibiting the same symptoms and upon inspection, the rear driveshaft support bearing/bushing was shot (rubber was broken) and the rubber mount on the passenger side of the rear differential near the snout had failed also. I replaced both and it fixed all the thumping...
First off, I'm aware of all the issues with the transfer case/PTO failures on the CX9 and I regularly check the fluid condition and level on my wife's 2007 GT with 147k miles.
Recently, I was under the car to replace the driveshaft due to the failed driveshaft support bushing/bearings and while...
I'm reluctantly starting a new thread because I have searched the internet and this forum high and low to find a write-up explaining how far the rear subframe/differential assembly needs to be disassembled in order to gain enough access to press all four bushings out of the differential mounts...