2004 mazda3 tranny viberates in reverse
 

guys need help! i get a viberation noise when i put my car in reverse....when it is in drive or park it is fine. what could it be?

search the forum for vibration issues. One recently was due to rocks stuck in the lower engine mount. and since it's an 04, there is also a recall on the upper engine mount - either may cause vbration only under load - or possibly in reverse only.