Originally Posted by AgRunner06
Ok so I'm guessing it's a grounding issue. Is it correct to assume that the problem is the ground for that one speaker (not the sub)? The noise doesn't come out of any of the other speakers so that would lead me to eliminate the deck.
There's no "ground" per se' at the speaker. While a a speaker accepts a "+" and "-" signal, the "-" side isn't the same as the chassis ground in the truck.
If the whine changes pitch with the speed of the engine, then that's typical electrical noise, and it's coming through the power lines. It can easily show up in just one side of a system instead of both. This is the weird thing about inductive noises.
To get rid of it, you need to isolate the power lines from the chassis which is done through the use of an "isolation transformer". One of the links at that Crutchfield link above points to this page:
From there, you can eliminate the antenna iso modules, so you're left with trying the line level iso's or the electrical. I would place dibs on the electrical side.
Given that this happens with the fuse pulled in the amp, I think that the noise is being injected at the head unit. That means you won't need a high current iso, so this one would do fine:
This will install in the + side of your power wires feeding the head unit.
It should fix the problem... if it doesn't, then the 2nd step is to isolate the audio, which would require something like this:
That would install betweeen the head unit and the amp. It may give different results depending on if you install it closer to the head unit or the amp side of your audio feed.
Sad to say, there's no real science that can be applied before spending money on devices to figuring this out. You kinda' roll the dice and try the options that are available one at a time until you get rid of it.
Sometimes you can get lucky and fix the problem by rewiring the power feeds, or re-running the audio feeds. The next time you're in your truck, set things up so you can hear the noise, then reach under the dash and see if you can change how it sounds by juggling the power wires. If you can change the symptom, you can fix the problem.
i.e., if you can change how the noise sounds by moving wires, then you've got a good chance of being able to get rid of it all together by re-running your power.