Back in a previous life when I used to do a lot of this sort of thing (installations of stereos, public safety radios, headlamp flashers, lightbars, etc),

I used to keep a fistfull of band pass filters laying around, and when I ran into this problem I would tackle it this way (sort of in order of priority). Some folks used to find a hot wire "somewhere" and tap into it for power. I used to run a fused, heavy gauge hot wire directly from the battery and make that my "source" --- pain in the keester, but well worth the extra effort. One could, even then, run the "source" to a second automotive fuse panel that one installs and have a "second" independent electrical system Been there done that (see keester comment above)

1. Find BARE METAL in the most convenient spot around, and drill a hole into it and CREATE an isolated ground to the chassis/body via a self tapping screw. Ground everything there. Forget "shared grounds".

Problem still there? (usually this fixed 70-80% of the whine cases)

2. Install a band pass filter "in line" in the "hot wire" line (see above).

This ususally took care of it.

Now, mind you, when I was doing this sort of thing, the "hot" set up in car stereos was ONE amp, and TWO heavy speakers somewhere (not true anymore). The anty has been raised multiple X since then.

AND, vehicles didn't have the electronics in them for EVERY single thing like they do noe. Hell, now I would bet there is a microprocessor for the ^&*( lighter plug......

But, then again, physics/electricity/DC probably hasn't changed since then, or since Newton was thinking about it... food for thought.

 

Kraut pretty much said it.

A common ground solves 70-80% of the engine noise problem. This means ground everything at one place, usually at the point where the most current draw is anticipated, the amplifier. Ground the head unit, processors, everything that supplies, modifies, or amplifies an audio signal at one place. Make sure it is to clean, bare metal and it is fastened tightly.

there are two common engine noise sources—mechanical and electrical. you pretty much ruled out mechanical by your description, so we'll assume it is alternator whine. That whine is caused by your alternator bleeding some alternating current into your direct current electrical system. "A/C Ripple" is usually extreme when the rectifying diodes in the alternator start to go bad. You can have one go bad, or all at once. Kraut's solution is similar to mine - place a 1mfd capacitor on the charging terminal of the alternator and connect to ground—the engine block ground is usually the best for this. The cap will send any of that a/c ripple to ground before it ends up being amplifed by your audio components, or radiated by a factory wire to your low-level connections.

Sometimes it is an old alternator telling you its about to retire.

An experienced, trustworthy installer is hard to find nowadays, and they are usually working on high-end custom jobs, leaving the commission-only monkeys to install quick radio & speaker jobs. Start by looking for a shop with MECP certified installers, then you ask questions, and pay AFTER the work is complete.

Good luck

 

Customer service is going by the wayside nowdays.. I'm only 18 and I am already seeing it.

As far as noise in a system, I posted a link that should've been made a sticky, search my posts for "ten commandments" and you'll find it.