electricblue wrote:...one sounds brighter than the other...
It's quite possible that the two speakers do have different responses. Every speaker manufacturer aims to get the frequency response of their speakers within a set tolerance window. The less expensive the speaker, the wider that rolerance window tends to be (and vice versa, of course). So with speakers sold individually, it's entirely possible that one might be at the low side of the tolerance window and the other at the high side, and thus the sonic difference between them relatively large, even though both speakers are 'within tolerance' as far as the manufacturer is concerned.
However, the other issue is the one Wonks mentions, which is that the acoustic conditions in your listening room and local reflections can make a huge difference to the perceived sound quality of each speaker.
What I would suggest you do is take both speakers to a large room -- or even outdoors if you can -- and place them, one placed above the other on a tall stand of some kind well away from the floor and anything else that would cause local reflections. Feed the same things to each speaker in turn and listen to see if they sound the same or obviously different.
If they sound pretty much the same then you have a room or local reflections issue in your listening space. In that case, do whatever you can to improve your listening area. Treat the mirror points with broadband absorbers. Move anything acoustically reflective away from the speakers -- especially computer screens. Ideally, there should be nothing between the speakers, but that's usually impractcial, so the compromise is that there should be nothing forward of the line joining the two speaker baffles (and further back is better).
If they obviously don't sound the same you either have a manufacturing tolerance issue or a faulty speaker. If it's a tolerance thing you may be able to get them closer by tweaking the EQ controls on one speaker, although they are often too crude to help very much.
An alternative solution would be to use a room/speaker alignment system like Sonarworks whcih will measure and calculate the appropriate correction curve to bring both speakers into the correct alignment, regardless of their starting position!
... includes some light distorted clipping on certain instruments, like electric guitar and piano.
Assuming you are sending sensible input signal levels, and listening at sensible volumes, this is more suggestive of a fault somewhere, either in one of the drivers, or in the amplifier electronics. Having one speaker slightly brighter or darker than another, say, could be put down to tolerance issues... but one having a significantly different level of distortion artefacts is rather more concerning.