Loud Clunk when shifting into reverse from park

2007 Mazda3, 1992 Miata
My wife's 2007 Mazda3 2.3L AT has developed a loud noise when shifting from park to reverse. The problem is worst during cold start-up. It is somewhat difficult to shift into reverse, then there is a loud clunk, the car shakes a bit, and there is a persistent rattle (sounds like the radiator fan hitting the shroud, but the fan isn't on). The noise goes away once the car is shifted into neutral or park. Doesn't seem to happen when in drive, although she said she heard the noise yesterday a couple times when turning. After a handful of seconds of the engine running the noise disappears.

A Google search seems to indicate a bad motor mount or maybe CV joint. The car isn't moving, so it seems unlikely that the CV would cause the rattling, but who knows. I checked the passenger-side motor mount, it seems to be intact. No oil beneath it, anyway. It was getting dark out, so I couldn't see the driver's side mounts well.

Any other thoughts on what it might be? What else should I check? The car might still be under warranty (need to check whether the extended warranty was 5 or 6 years), so a trip to the dealer may be in order.
2005 Mazda3 sport 5spd & 2013 Mazda3i Touring
sounds like you have a bad transmission mount....they usually clunk going into gear and vibrate while in gear also
07' Mazda 3 and 04 Mazda Miata
Hey Ya'll!! Got a question about this same issue here in this thread.... I'm hoping someone out there with experience can help edu'micate me to figure this out. I just found this mount broken again on our 07' Mazda 3 (2.3L non turbo). Any suggestions on what may be causing this?

I replaced all three mounts on it six months ago. I did use "Autozone" parts though. Nice thing is,... they are still under warranty but I would think they should last longer than six months! The big one on the passenger side and the rear one were both broken when I looked for issues six months ago. That's why I replaced all three. Thinking maybe the third one would be not long for this world after the other two had been rattling around for probably a year or more. ( I don't drive it very often.)

Thanks in advance y'all!
2005 Mazda3 sport 5spd & 2013 Mazda3i Touring
you replaced it and it broke again??
how you driving it??
was everything assembled correctly.....(not to doubt your assembly) did anything seem difficult to assemble like a mis-alignment maybe