2004 Mazda 3 S Hatch, 88K, auto trans, recently developed a shuttering/vibration under a load only. at idle no problem, runs smooth. when you put it in gear there is a bit more vibration than at idle both reverse and drive I've seen some posts already on engine mount problems. is there a way to determine if the #3 mount is bad with out taking it apart..can you jack the motor to see any separation in it? The top mount on the passenger side seems solid when in gear no obvious abnormal movement.

 

look at the mount when moving, like slowly in first with the hood open.
It's possible the clutch or something has been damaged too... or is it smooth when idling in first for example?

 

pulling away slow no problem at all..I had my son in car w/ it in gear (auto trans) to rock motor around under stress looked tight..Even rocked the car back and forth by hand to rock motor nothing obvious like a V8 broken mount. However there is some slight dripping oil around the passenger mount, noted down the side of shock tower area that I thought was odd.(not realizing they have oil in them) but by no means does it look shot..It idles smooth, no vibration reving engine at all in park, appears strong and when placed in gear there is a slight vibration, both in reverse and 1st. I have not looked at trans mount yet under battery box...Vibration occurs after 2000rpm and at times can be almost normal. but the shuttering that goes on is quite a rumble when you try to get on it. I put new struts and new pass axle (thinking it felt loose..wrong it was fine).. ball joints are both tight, sway bar links tight..when going over bumpy side roads it sounds like the ball joints are shot on passenger side. I am really hoping after reading all the posts on the mounts that this is the issue.

 

There was a recall for the motor mount through 06 models I think... but the leaking mount means that's likely the problem.

aah, memory served me right - see http://www.finishlineperformance.com...35-07-1844.pdf

 

I replaced passenger side #3 motor mount..it couldn't have been more destroyed..on the outer appearance it sat in it's saddle ok even when lifting the motor..but once I unbolted it was in 2 pieces. This should be a recalled part. Car drives like a normal car now. no "suspension" clunking over bumps and all vibrations are gone. Was in in 10 minutes.

 

Glad you found the issue, and that it was a quick fix.
I figured it would be an oily mess since you mentioned there was an oil leak around it...