Upgrade you battery to chassis cable and your alternator to chassis cable.1) How to eliminate noise from the line driver.
Failing that could be a poked line driver in which case you;re probably better of replacign than wasting time trying to repair it.
Use shielded co-ax RCA cables if your system (presuming your system uses unblanced inputs/ouputs)2) How to shield my cables
Can't sheild DC power cables so don't bother trying.
I wouldn't bother3) How about a small capacitor?
See reply #1.4) Other things that worked for you