Hi James,
I might be on to something, but it may be common to all the units.
When I put my BCD-1 into standby, and this is repeatable, four to five seconds later you hear what sounds like the the capacitors discharging, this is what I'm experiencing while playing a disc, but louder and sharper.
If anyone has the time to try this and report back it would be greatly appreciated, if it's common with all the units them I'm back to square one, if not it may be the heart of the problem.
Robert