Floating or common ground?

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Trying to get rid of alternator noise.
My setup is this:
HU Pioneer dex-p99r(the old one)
Amp Velocity by Blaupunkt VR6000, a six channel amp.

Measuring resistance between chassis ground(negative battery) and phono input/or negative speaker terminal on the amp shows 1K ohm.

Measuring between chassis ground and rca shield is 1 ohm coming from the headunit
(it has 1 ohm resistors used as protection?)
Measuring between two rca shields show 2 ohm.

Does this mean that the headunit have common ground and the amp not?

Measuring between HU chassis and ground shows open circuit.
 
It´s very low but still annoying. Most noticeable when starting engine and volume all the way down. It follows the rpm.

Uploaded the manual, on page 63 is the preout diagram I think.
filehosting.org - download page for pioneer_deh-p945r_dex-p99r_1_.pdf

Amplifier gain is not set too high, it states 8v fully clockwise on the amp, the dex have 4v preout and pot is set halfway.

I could try to groud the HU at the amplifier for starters. But why is there 1K ohm between rca shield on amplifier input and ground?
 
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I have a 6 channel rca triple shielded run on opposite side as powercable. Recently changed it and got rid of static/motor hum from the heaterfan.

Tried grounding the HU case, no difference. I´ve read something about common ground and floating ground components not function properly togheter.
 
Car audio equipment is almost completely immune to ripple/noise on the B+ line. A capacitor isn't likely to make a difference. I'm posting this because I don't want everyone with a bit of noise to go waste their money on a capacitor.

Generally noise is produced when there is a defective or poorly designed piece of equipment or the audio signal lines are too close to a 'noisy' component (sometimes the ECM or other 'computers').
 
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