We need more info. What receiver? Does it do this on all sources? What speakers do you have? Most people out of the box run their subs way too hot anyway, what gain level do you have your sub at?
Possible issues-
-Center channel is not wired right or is loose
-Receiver's volume setting to center is way too low compared to the other speakers
-center channel amplifier is shot
-center speaker is shot
Get a test/setup DVD, or run your receivers test tone, and make sure you get the same output (or reasonably close) from all 5 channels. Obviously it is better to do this for your problem if you can do it from within the receiver, because then you can take out the possibility that the screwup is coming from the signal into the receiver. If the test tone is equal across all channels, then go look at your sound levels in the receiver, you may be running your center at -10 or something goofy accidentally.
It could really be quite a few things...for instance some Klipsch speakers are 102dB/w, if you happened to have a Klipsch L and R, and a different speaker from Infiniti as your center that only gets 92dB/w, that would cause a similar problem. Come back with your equipment and more info, and run the test tone, and let us know how it sounds.
