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well, then how do you can i explain my multimeter working correctly for batteries and resistors, but not reading my car battery correctly?

Yeah both the voltages you posted can't be true. If your alt or battery was putting out that much it would freak your cars electronics out.

Yeah it might be working for smaller voltages 1.5 or so, but its off above 10 or so.

that makes less sense to me than the battery outputting a high voltage. i've measured it at the amp, at the battery, and at the HU. At the amp and HU, i get 17.9 volts, at the battery i get 18 volts. i'm getting it inspected monday, and I'll have then test it.

Most electronics can't handle 18v, only up to 16v. So if stuff is turning on, then it isn't 18v.

i just measured the voltages for the cigarette lighter, and dome light, both measure ~15v. I really doubt this meter is bad, considering it's relatively new. The voltage could explain some of the odd behavior i've been getting from my HU.

Dude, the meter is Bad. Trust me, I use a fluke EVERY day. Heck even if its an el cheapo its reading 3 to 5 volts high. Thats WAY out of limits.
I bet it will read over 120 if you test a wall socket.

So, back to the topic of the post, the noise. I disconnected the RCA's at both the HU, and amp. The amp was only connected to the HU by the remote wire. When I powered up my HU, the noise was still there. So, the noise is coming from the amp. I disconnected each speaker channel, individually, to rule improper speaker wiring as the source, and still, noise was produced over the channel that I left plugged in. So, the amp is causing the noise, due to a bad ground? I don't know how to make the ground any better than it is, there's bare metal, I can't sand it any better, what else could it be?

Bare metal doesn't always consist of good ground.
You need to have it on an inner structure piece.
Tap welded metal like body parts ussually make poor grounds.
The closer to the frame or unibody the better.

And I had a tester that did the same thing so the tester is bad.
With your car running your battery should show around 14.4

cargodz wrote:Bare metal doesn't always consist of good ground.
You need to have it on an inner structure piece.
Tap welded metal like body parts ussually make poor grounds.
The closer to the frame or unibody the better.
And I had a tester that did the same thing so the tester is bad.
With your car running your battery should show around 14.4

yea, I was curious where on the frame was a good grounding point. I'm not certain which part of the chasis is best, I guess I'll just try different spots. If it isn't a grounding issue, what else could it be, hypothetically?

Anywhere on the frame. The frame is the grounding point for electronics on your car. Just keep your ground wire short. For noise, as far as I know, a bad ground is the only reason.