My car started shaking a couple weeks ago. Only while stopped and it was worse with the A/C on. It was idling perfectly, so I did a little internet diagnosing and it seemed like all signs pointed to my motor and/or transmission mounts. I do a little bit of maintenance to my car here and there, but this job seemed a little daunting to me, but thankfully it was actually pretty easy! That is until I got to the transmission mount. It was in really bad shape. It was barely hanging on. Not sure if it's just age, or what, but the bolts looked like they were hanging on for dear life. One of the mount to transmission bolts came out perfectly, the 2nd one came out, but was bent and upon closer look was actually at the breaking point. The 3rd one... was broken in half. I'm not sure if it was already broken or if it just snapped when I tried to take the bolt out. I panicked a bit, and decided to try taking it out with a bolt extractor (which I heard can be hit or miss). Thankfully, it worked. The motor mount was worn and the rubber was torn. The transmission mount didn't look too bad, aside from the bolts, but they were both replaced with OEM equivalents. Maybe later I'll upgrade them, but I'm not looking for more NVH, so I went OEM for now.
Almost forgot, the mounts solved the issue of the shaking. It's so much smoother when starting up the car too. Shifting feels a lot better too (Obviously!).