Well, i have a 1999 Honda Civic Si, recently replaced both axles new, and now the car vibrates between 25mph - 35mph,

under 25mph - no problems
when its 25-35mph - vehicle vibrates
over 35mph - hardly noticeable slight vibration...

it is only when accelerating.. the wheels should be balanced cuz they are about 2 months new...

what could be my problem...

bad axles or needs alignment?.. the car is out of line, and does glides towards the right...

 

tires are out of balance, check the tread wear

 

i dont know how bad your vibration is but...

i broke the passenger side halfshaft at a recent autox. the oem one had the damper ring on it also where the axle snapped. i put a napa one on and it didnt have the rubber ring on it. when i first drove it there was a slight vibration around those speeds if i remember right..but they are now gone.

 

I would say unbalanced tires or bent rims, BUT you mentioned it is only when you acelerated which eliminates those. Whether they are bad or not i do NOT know but I def say there is still something going on with the axels.