You're getting noise because you are connecting two headunits (via the RCA's) that are not at the same electrical potential. Therefore current is flowing through the RCA connections. That's what we're going to eliminate by process of elimination....... did that sound weird to you too ??

just commenting in case it is helpful...

lastdan: im not sure if youve already passed this hurdle but, have you eliminated the empeg as the source of the sound? ie, just wanted to suggest running the RCA cables from the empeg, off to a portable stereo or home stereo, and see if the whine is picked up there (ive done this to troubleshoot my own unit, parked in garage and run RCAs to my room to listen to the output) it will at least tell you if the loop is coming from the empeg, or elsewhere (amp wiring)...?

justin: if youre not getting alternator whine (or other electrical interference) then i dont think it is a ground loop issue? just my first thought - going on wild goose chases ripping up ones dash is no fun, as i know

if youre not getting alternator whine

If you reread my posts you will see that I already mentioned that I do have alternator whine. The noise changes pitch with the engine's rev. But, the noise doesn't disappear when the engine is off.

much like my problem. but the alt noise may be caused by the same problem that makes it noisy when it's not running (I'll live with that, if i can)

please let me know if you all get a little 'drive' noise, even if it;s no biggie. boot up is most noticable.

Fuel pump noise? Probably RF radiated? Needs a suppression capacitor?

please let me know if you all get a little 'drive' noise

I already mentioned that I have this problem, too. And it's just as noticeable as the "alternator whine."

Edit: It looks like I've hijacked your thread... I apologize.

Fuel pump noise? Probably RF radiated? Needs a suppression capacitor?

One suggestion from someone I know was that it's possible that my high output alternator is causing noise on the constant power line of the empeg. The direct line to the battery passes within 18 inches of the alternator; possibly even closer. I tend to overestimate measurements.

I never heard the term suppression capacitor. But someone suggested a power line noise filter, if it is determined that the noise is coming down the empeg's constant power line.

The ones at Radio Shack are reported to have bad frequency response specs,......
Any idea what the specs are? Is it primarily bad in the upper or lower spectrum?
I have, I think, the inline RCA fground noise filters you're talking about with the big black pill shaped filter in the middle. I use this on the powered sub.

Alternators are supposed to be shielded, since they would otherwise fail RF tests. Unless the casing of the alternator is not earthed, this should not be an issue.

Alternators generate noise if the regulator is damaged. If you ran the engine without the battery or a load connected, you could have damaged the alternator.

It is more likely your battery is going high impedance, and if it is being force charged by a "hot" alternator, then the fluid levels may be low. Check and top up with distilled watter, or have the electrolyte checked at the garage.

A suppresiion capacitor is a high voltage foil capacitor used to short circuit noisy devices such as ignition (breaker type), wiper motors, AC motors, etc. They are common at spares shops.

A power line noise filter is likely to be an in-line coil filter, installed in line with your main power feed to either the empeg or your amp. The empeg already has one built into the harness.

You are just a wealth of information. After taking all of that into consideration, this is all I can say:

I doubt it is the fault of either the alternator or the battery, as both are brand new; recently installed and tested by my mechanic, whom I trust.

I'm not sure what to think about a supression capacitor, as I've never seen or heard of it before new and so don't know how it's used. And as for the power line noise filter, is it possible that there is so much noise that the empeg's isn't enough?

But anyway, I've decided to put this on hold. The noise isn't audbile until high volume levels, and I find that cleaner sound is important to me. So I will not turn it up very loud if the sound gets too dirty. So this problem will wait until I put in my amplifier, which should be soon. Hopefully.

Thanks everyone for help and suggestions. I will keep this thread in My Favorites so that I can use it later in order to nail down the ground loop when I do the amp install.