Having a strange issue that I can't seem to find anyone who's had the same problem.

Many people have static/popping all the time or randomly. Mine pops when I turn the key.

The speakers only pop when I crank the engine to start any other key position doesn't case the noise.

The sound comes from all the speakers in the car.

There is no water leaking in the trunk and all the wiring in the doors and the black trunking is perfectly fine.

The audio system I have is the tape deck with disk changer in the boot. Non dsp. Full screen nav unit. I think it's a mk4 unit.

The popping occurs most of the time probably 1 in every 6 starts will be quiet. Otherwise the sound quality is fine and no popping of speakers other than on start.