So, this just started happening in the past month or so ago after about 1 year of flawless performance... This is what is have: Z1, Alpine 4x150 Digital Amp, MTX powered compact sub.... Amp and Sub wired via 6Gauge to the battery ground to the car (making sure i have a good ground)...

On occasion i get a slight alternator whine (very slight)... I thought it was possibly caused by the sub....added an RCA ground isolator and made little or no difference. Now, i added 2 Ground isolators to the Alpine Amp (2 of them because i;m using 4 channels) and now the Alternator whine is much louder and happens all the time!! So, needles to say, i removed the isolators... the whine is very slight and *could* live with it, but dammit!

Any ideas about what this may be symptomatic of?

P.S. i even changed the RCAs to the amp to ones with better shielding to make sure it was not caused by inductance.... guess it could still be inductance from 6Gauge power being to close to speaker wires???? Is induced noise (due to inadequate shielding) a typical problem for car installs?

Have you tried grounding the shielding on your RCAs?

To be honest it almost (I do mean ALMOST) sounds like the gain to the Alpine amp are turned up a bit much. Since it is difficult enough to troubleshoot a noise problem in my bay, I will give you a few pointers of what I would look for.

When you use the system, is it really loud at volume levels 20-30?

Does it seem no mater what volume level you are at (again 20-30) does it seem to not get much louder?

Does it sound like all he** breaking loose above that?

If so, then you may need to turn the gains down. Sure, you will have to turn the volume to a higher number to get the same loudness out of the system, but your noises should be gone.

The reason the ground loop isolators made the noise worse, is you don't have a ground loop. At worst, I think you may have a noisey-ish power path somewhere that is being overamplified.

Hope this helps, just remember- A car is a terrible thing to waste.

GOOD CALL MARC

I think the amp gain may be the culprit, i will check it out this weekend.... I definetly thought the gain was a bit high since i can hear a very slight distortion.... it's kinda agrevating to have a 2K head unit without 5V outputs......

Do you have a empirical way to set the output levels correcly? like measuring the output voltage from the amp as it relates to the volume setting on the HU? I have a disc that outputs constant tone for voltage measurements, but don't know of a good way to apply the same techniques to a car HU

Thanks!

P.S. do ferrite chokes on the power/ground make any difference in Car installs to remove RFI/EMI noise? BTW, i have n Alpine PDX-4.150 amp... amybe you have a std setting for these with the Z1/2...

Just a quick followup.....

I droped the gain on the amp..... it made a huge difference.... still had a bit of hiss from the head unit, but the whine was gone... thanks for the tip.... I then re-routed all the wires and separated the power/grounds from the signals... I added some ferrite chokes to all power/ground cables in the system.... The final results of this 3 hour effort is a dead quiet system.... very happy.

Thanks for the advice.

Another thing to consider when alternator noise develops out of the blue, is the alternator itself. A diode could be failing. When that happens, the alternator becomes very noisy as the current chases itself around inside the alternator. This noise should be more prevelant when the battery or car calls for a heavy current...such as right after starting the car. Just something to keep in mind.