how did you add a sub? in a sealed box? what kind of music do you rock?
sealed box is going to give a lot of low end bass. ported box, geared towards rock.
this is not always rule of thumb but some people grab a amp and a sub in a sealed box and you end up with over powing the main stock system. lots of low end.
some capacitors on your full range speakers and bumping the amp x-over to 150hz may work but it all depends on your individual setup.
i live by cherry creek resv. work in the dtc.