under the passenger footwell apparently.

i dont own a crossfire so im not too sure.

under the passenger footwell, pull up the carpet, remove the foam, unbolt the metal plate and it should be there..

have a look at the gains of the amp (with some amps, left and right have their own gain adjustment)

will be worth having a look..

also have a look at the hi/low level imputs (AKA RCA's if it uses it, or just the wires going in)

ive had a problem before with a broken RCA and noticed that with only 1 RCA plugged in (right) the left speaker will still put out some sound (very little)

so either way.. have a look at your amp.