The only explanations are something has CHANGED or something has BROKEN.
I will do some test clips .
Failing that, I will borrow a laptop and see if I have the same issue.
Thank you both again.
Later: Got message that I can’s send any more messages yet.
I think we’ve cracked it… I think this sounds A LOT better… with microphone/boom/cable moved away from the back wall (with power socket/metal-backed insulation)