2005 peterbilt with ignition off NO noise turn key to acc. position all kinds of static.I unplugged coax from radio noise is gone.Its a diesel engine so mechanical fuel pump.It does it when all the accecorys off even headlights,heater fan, sterio,as long as key is on so is the noise and I can hear it in the background when I recieve.Sounds like a helicopter in the cab I'm lost here.The truck does have a factory stereo amp behind passenger seat but like I said even with it off I still here the noise.Every so often I can turn the squelch down to normal but that is few and far between,and I watch guages to see if engine fan or something but to no avail.Could it be alt noise possibly?The only thing I could relate it to was I have one faulty guage in truck( fuel psi )and the needle goes nuts back and forth almost in sequence with noise but it is not a electical guage.Anyone?