A few possibilities I can think of
- You do indeed have a speaker that's not working properly - try putting the left speaker on the right and the right speaker on the left (and wire it that way) and see if your problem now
- they are in fact different generations of the same speaker - infinity may have made crossover/driver/etc design modifications that aren't readily visible.
- your computer software has some balancing issues
- your 3.5mm out isn't in right
- a wall on your left is causing reflections?
the only way to really find out what your problem is to isolate it.
-Try adjusting speaker placement, preferably equally and well away from any walls
-Try both of the speakers on different channels of the receiver not only in stereo but also in mono
-see if both speakers are equally stuffed with dampening material - the "refurb repair" shop may have accidentally taken one set of dampening out. This is easy to replace if it's the case.
-Give both speakers the "knock" test to see if they're equally inert. They should be, but you never know what's gone on
- Try different inputs to your receiver, not just the computer