Different sound between two channels

I have noticed recently that the sound of my left speaker is slightly different than my right speaker. The right channel appears to be brighter sounding than the left channel with the right channel sounding slightly richer sounding. I've tried reversing my speaker cables at the back of my Pass X250 and the problem kind of switches channels. I'm not sure if the problem is with my Hales T5's or the Pass X250. I think it may be a bit of both. I replaced the voice coils on both the tweeters of my Hales and the sound in general improved but the issue of the right channel being slightly brighter remains. The difference is noticable with the entire speaker as when I play just one channel or the other I notice this characteristic sound with the enire speaker. If my preamp is muted I will get a bit of residual noise from the amp in my right speaker(which is the brighter sounding speaker) and I imagine this residual noise is constant and may be causing the varient sound between the speakers. If anyone has any possible explanation or similar experience your feedback would be appreciated. I should mention that I spoke to Pass and they said it was normal for the X250 to be slightly different between it's two channels and that some residual noise in one of the channels is normal. I should also mention that what I'm experiencing is only noticable when listening right up to each speaker and is not noticable from my listening position.