Whine in the mid's and highs

My roomate and I pretty much finished up his truck last night about 1 AM.  I noticed a small whine in the Mid's/highs, not alternator noise as it happens with the vehicle off,  the noise rises and falls when I adjust the gain.  The Grounds seem to be good, i.e, all going to the same place to a good ground location.  The amps and crossovers are all used, from my old system, could it be possible that the board is bad on the crossover?  Im not sure what else it could really be  =(.  Anyhow, its 2 old PPI art series, and the crossover is an audiocontrol 4 xs.  I'll try different RCA's today, haven't done that yet,, not sure what else it could be though =/

~Jay

Ill give that a try too when I get down to the shop,I can't recall this noise in the last vehicle it was in, same amps + X-over, the only thing different is the HU, my roomate has the CD 5444, whereas in my old vehicle I had an alpine =/

~Jay