Another issue could be the cantilever on your cartridge is out of position. This could be caused either by mishandling or defect in the cartridge.
Get a pair of magnifying lenses and look at the cartridge straight on from the front. The cantilever should be evenly positioned from left to right in the cartridge body with no tilt on the stylus. If it appears off, this could be generating the volume difference since the far end of the cantilever will be out of position inside the body of the cartridge.
If this is the case, sometimes removing the stylus assembly and reinserting (if removable) will correct the problem. Otherwise you might need a new stylus assembly.
Also check the weight and anti-skate settings on your tonearm, and double check the overall alignment.
Get a pair of magnifying lenses and look at the cartridge straight on from the front. The cantilever should be evenly positioned from left to right in the cartridge body with no tilt on the stylus. If it appears off, this could be generating the volume difference since the far end of the cantilever will be out of position inside the body of the cartridge.
If this is the case, sometimes removing the stylus assembly and reinserting (if removable) will correct the problem. Otherwise you might need a new stylus assembly.
Also check the weight and anti-skate settings on your tonearm, and double check the overall alignment.