For the last little while, I've been having an awful case of alternator whine. When the empeg was out of sled, I got none. When the empeg was off, I got none. When the empeg was on (even paused), I got the whine. I discovered that one of the -ve speaker wires had come apart, and was no longer connected. A few weeks ago, I spent some time soldering all the wires onto the connectors (as opposed to just crimping). That didn't work. Today, I checked the grounding. There was still a lot of paint between connector and frame, so I sanded that down to bare metal. Still no luck. I gave up, and put everything back together.

After that, I decided to adjust the gains on my amps, since they were far too loud for normal listening -- most of the time, I had the empeg volume nearly as low as it will go. After adjusting the gains, and turning the empeg up a bit closer to 0dB (well, it's now just past the middle, so that I still have some room to go up, if needed), I seem to no longer hear any whine. Empeg out of sled, no whine. Empeg off, no whine. Empeg on and paused, no whine. Empeg playing, no whine.

So... does this make sense? Did the previous position on the gain controls just mean that the electrical sensitivity was such that the extra whatever from the alternator was causing problems? The problem seems "fixed", but is it really just "masked"?

(Pardon my lack of use of appropriate terminology, but I don't really know anything about electrical systems. )

Yes, what you said makes sense. Specifically, this:

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most of the time, I had the empeg volume nearly as low as it will go

That means your amplifier gains were cranked way way way way way too loud.

Remember that all audio systems have a noise floor. By cranking up the amplifiers so high, you were simply amplifying that noise floor. All you've done is adjusted things properly for once. Poof, magic, now it sounds right.

Setting the amp gains properly is one of the first steps in troubleshooting a whine problem. It's in our installation FAQ as well as in pretty much every other noise troubleshooting guide I've ever seen.

Also, based on this statement:

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and turning the empeg up a bit closer to 0dB (well, it's now just past the middle, so that I still have some room to go up, if needed)

At that point you could still stand to have the amp gains set even farther down. The ideal, best quality signal will be had when you are able to turn the empeg all the way up to 0db and that is exactly the loudest you would ever want to play the stereo when you're at 80mph on the freeway.

Quote:
The problem seems "fixed", but is it really just "masked"?

No, it's actually fixed. Like I said, all systems have a noise floor. You were just cranking up the noise floor.

Luckily your problem was easily fixed. Some cars seem to have lots of wiring weirdness. Alternator , battery, general wiring are usually things to inspect when you have these problems.