Crossover for Components picks up noise??

I have a 2003 Nissan 350z and I just installed a set of MB Quart QSD 216's.  The problem I'm having is that no matter where I place the giant crossovers, with the key in the on position, I get a high frequency noise that I issolated to the crossover.  Even with the source lines disconnected, the crossover is picking up and producing noise.  Obviously when I disconnect the speaker leads from the crossover, the noise stops.  I suspect that it must be picking up frequency from the speaker leads that I ran through the very tight factory wire boot from the door to the kick panel; when I move the wires around near the exit point of the harness to the boot, the noise seems to get slightly quieter.  The sound is not loud, but very noticable and is coming out of the woofer as well as the tweeter at about the same frequency.  I was trying to avoid installing the crossovers on the doors, though there is room, due to the fact that I would like to be able to easily adjust the db levels for the tweeters and that requires disconnecting and reconnecting a bridge on the terminals.  I have moved the crossover to different spots, though not a great distancr from the dash, and the noise continues at the same level.   Are there any ways to fix this without compromising the sound quality?  Is this a common problem with crossovers?

Are you using the OEM wires or did you install new wires into the system ? I suggest running new wires to the speakers from the crossover's straight from the amplifier instead of using the OEM wires that can pick up EMI from the vehicle.

I used new wiring and fished them through the factory rubber harness and gasketed socket.  I had to boar out a bit of space after fully dissasembling the socket.  I just today called my buddy at Innovative Audio, and he said that it's common to pickup ignition noise from the crossover even when the engine isn't running, just like what I've got.  So I spliced in a long line and moved the crossover around the car to see if it got better.  The noise is gone if I keep it a good distance from the dash.  I'd like to install them in the passenger kick panel if I can figure a good way to shield either the crossovers, or the car's main wiring harness.  I'm going to pick up some shielding tape tomorrow and see if I can shield the harness, otherwise it looks like I'll have to relocate the crossovers farther back in the car.  If anyone knows of any other good ideas, please let me know.  I'll try the foil too and see what it does.  Thanks.