So I posted before about there being a high pitched, loud buzz/whine after putting the cr back together. The suggestion was to solder the connectors in the passenger kick plate. Was going to do that eventually... But, events yesterday:

Wanted to replace the door check in the passenger side as it clicks badly. Had a replacement and installed it but the clicking was worse so put the original back on. Of course, removing the door car means unplugging all the speaker, disconnecting the woofer to get your hand in.

Reassembled and randomly tried the radio - no more buzz! Crystal clear sound and general excellence. Brilliant!

Got in this morning to nip to the shop... Buzz/whine is back.

What on earth is causing that? Given the kick plate and connectors weren't touched at all, surely it must be something else?

Check the connector on the door amplifier. They corrode as well !!

Buzzing or whine are generally either ground faults, or one side of the balanced pair open circuit.