When the front diff. mount breaks, ala this thread, will it effect the ride quality? I have that issue and also, the car rides like I'm driving on rumble strips above 40mph. I'm trying to figure out if the broken mount is the culprit or if I need to look at something else.

 

If it's just the front diff mount that's broken, the car will feel perfectly normal unless you're getting on the gas hard or abruptly downshifting. The nose of the diff will jerk up and down when power is applied.

http://www.mazdatrix.com/g2.htm

The rear u-joint on the driveshaft may be toast.

 

that def sounds like the rear u joint

 

It is definately an imbalance of something. Would fix what you know is broke and then if you still have the issue look elsewhere.

 

It does appear to be the U-joint. From some of the other threads I've seen I assume that the U-joint replacement available from Advance Auto is pretty much useless and a replacement shaft from Mazdatrix is in order?