Dear @edgewear: Like Spencer sid seems to me groun problem tht could be nywhere from the Reed tonerm female cartridge connectors to the IC cbles connectors. Somewhere in between exist a " cold/loose solder tht sometimes is ok nd sometimes develops the problem. So you need to check ll the wiring/IC cbles connector termintions trying to look for tht ground problem. The orienttion/position of the IC cbles could help little but the problem will not disppears totally. You need to check those contct connectors including the tonerm ground one.
R.
R.