All amplified installations are prone to noise these days. The fact that you're running a low level RCA signal cable through a vehicle where, in all probability, the manufacturers paid virtually no attention to RF shielding except around important electronic equipment unfortunately makes interference inevitable, unless you're very aware of some important points.

Generally, but with the Empeg in particular, the following is all important:-

1) RCA cables need to be run away from all original factory wiring in the vehicle - preferably at least 12 inches, but in places where it's unavoidable to cross orignal cabling, make sure that you run RCAs straight over the original cabling at an angle as near to 90 degrees as possible. If you run RCAs parallel to any original cables, inductive pickup can occur, resulting in the amplifier 'seeing' any noise in the factory cables and amplifying it.

2) Grounds all need to be at one common point. If the Empeg's cage comes into contact with metal around it's dashboard mount, then it'll see an earth there - so make sure that the amps all earth to that same point. If the Empeg bracket isn't touching metal, then you can get away with earthing everything to another point elsewhere in the vehicle - but do make sure that the amp(s) can't see earth through their own chassis, by mounting them on a non conducting material (ie. MDF, etc)

3) Make sure all power cabling is sufficiently sized - we see endless installations with woefully inadequate cabling. Earth an amp using a cable that's too small, and it'll try and earth through it's RCA shield - when that happens, there's a risk of both damaging the source unit, as it's RCA output stage probably isn't designed with high current demands in mind, and you'll probably induce noise. As a rule, for any unit, establish it's peak current demand, then use a cable with 1.5 - 2 times that current rating.

4) Specific to the Empeg unit, make sure that the inline choke is fitted well away from all the other cabling, especially the RCA cables. If it's mounted in close proximity with another cable, the two form what basically amounts to a transformer, and any noise in the power line gets induced into the signal to the amps.

Hope all of that's of some help. If anyone has any specfic noise related questions, feel free
to contact me directly and I'll be happy to try and help :-)

Dominic

Cambridge Car Audio
http://www.cambscaraudio.co.uk