popping sound from speakers/common ground

'87 BMW 325i (M20 engine, E30 chasis):

Installed Pioneer DH4700 using factory wires, amp, and speakers. Car uses common ground design. I connected all the positive speaker leads to the corresponding speakers of the car, leaving out the negative leads.

Memory, Battery, & Ground wires were verified with a multimeter along with ignition position.

Radio retains its memory, functions with the ignition, and antenna goes up & down with relationship to radio power.

There are two white wires that lead to one, which appear to be original (soldered and heat shrinked). Only when I connect it to the "remote" wire of the hu, is when I get sound from the speakers AND is when the antenna rises.

Note: no popping when remote wire and car's white wire(s) are disconnected because the white factory lead wire has both the factory amp turn on and antenna leads???

POPPING SPEAKERS takes place during two events: 1) slightly audible - when the radio is powered on, either by ignition or manually by "src" button. 2) much louder - when the radio is powered off, by ignition or by head unit, and appears to be isolated to or appears to come from the FL and RL speakers.

How can I get rid of this popping without wiring direct from hu to speakers? The speakers have 3 leads, which is the correct + lead for each speaker for the hu?Are the popping sounds occurring because the neg. speaker leads from the hu are disconnected?

Thank you very much in advance