Static noise from radio

Car: 2004 Suburu Outback LL Bean Edition

Problem: radio emits strong static noise when car engine is on, but reception is clear when engine is off. Ongoing for >year.

Original Radio: Alpine radio with retractable GPS

Actions to date: 1) Audio system examined twice by Suburu and Alpine mechanics, each claiming that the problem arose from the other’s domain. 2) Suburu replaced aerial pre-amplifier, but with no improvement. 3) Best Buy removed & upgraded old Alpine unit to Pioneer AVIC-U310BT 4.3 radio/GPS and replaced all wiring. Radio static problem remains while iPOD amplification is crystal clear and GPS works fine.

Please HELP

Two sources of this static are the ignition system and the alternator. There are suppressors on the ignition system as a spark transmits a signal across many frequency bands. Defective spark plug wires might be a cause. As far as the alternator is concerned, the slip rings may be generating interference. There also may be a bad diode and the alternator is superimposing alternating current on its direct current output.

Many thanks. I will go back to the Suburu mechanic with your diagnosis in hand and report back on the results.