In my case, I got crackles and pops (over bumps) or generally when on the move: I also on occasions lost channels completely.
I opened the case and found that the earth/shield wires of the audio harness towards the rear of the unit had broken off from the board connector, probably fatigued. The wiring bundle was badly routed (one of Hugo's complaints about how the Mk1 was made) and the disk sled rested on them and put them under tension. Net result - snapped wires, no audio.
I used an especially fine (0.5mm) soldering iron to re-solder the shield wires after carefully re-arranging the wire bundles to give more space under the sled at the back of the box. This meant unsoldering the "at home" output connector wires briefly, but this is not a big issue if you are moderately competent with an iron. I have been crackle and audio loss free for about a year, with only a single re-occurence of the same thing on the remaining shield wire that broke later on.
While the box was open, I took the opportunity to properly glue in the disk shock mounts with epoxy resin glue; since I think it is the sled clouting the wiring harness, I am now more confident that both the disks and the harness will survive for a while yet.
If you are not confident, I would suggest dropping a line to Hugo to see if he would be interested in applying his magic brand of TLC to your harness.