alternator noise is more of a whine that goes up in frequency with RPM.. ignition noise (spark plug wire) is a ticking noise that gets faster with RPM..

If you are fighting alternator noise and can run it while troubleshooting I would get some jumper wire and start jumping all the ground points back to the battery the stereo is fed from.
these include the engines as well, both of them. just watch your fingers around the serpentine!!

If its ignition try moving the plug wires around while its running
if one bites you or the noise changes you may have found your gremlin.. again watch your foreskin around that serpentine!!

Good Luck!!

bobbo

If you can hear your stereo with the engines running then your engines are way too quiet and that is the problem.

def a whine, I'll have them do the wire off first and if that eliminates it, I'll do the ground test and prob put in a capacitor as well.

When I used to mess with car stereos that amps installed if the speaker wires where near or touching thenpowermsupply wire it would cause the noise you are describing. Try separating your wires before buying parts and taking the whole system apart

Or your going to slow, at 80+ even with 800 watts of power, I can't hear my stereo at all.

Brushes could be getting bad on your altenator, voltage regulator getting noisy, feedback from ignition module. Put a scope on your 12v at the radio and look at the frequency of the noise. That will tell you the source. If no noise on the power is noise heard with tuner and other inputs or only one? Could be input filter cap on the radio. Either way a good cap on the input power is a great way to filter noise and help bass response.

You may need one of these:

http://www.parts-express.com/pe/show...number=265-012

Normally a good stereo has one in it but it may have failed, for 10 bucks it is worth a shot.

+1

I had the same problem you are having. ran all power wires (+ and -) direct to the battery and problem gone.

it was the alternator, new one being put in today..also gonna run a capacitor ...thanks for all the help and good ideas. I learned quite a bit

I don't have any special sound system but for me the music is just a distraction when driving the boat, and I can't hear it anyway. It just adds noise. Anyway, if OSD likes to cruise or idle with the jams on then I can understand the whine being annoying.