Yes, it's more than a problem, it makes balanced drive impossible. But the symptom is not hum; it's left channel dropout, which suggests an intermittent problem in the hot side of the L channel. Since it is intermittent, such problems are often difficult to isolate, and the finding of continuity with a tester can be misleading.
Diagnosis Help: Left channel out, turntable ground leads crossed somewhere
I recently acquired a Thorens TD 145 turntable. I have an issue where the left channel often does not work. I isolated the issue to the turntable itself. I got a voltage meter and found cross talk somewhere from the tonearm (with the headshell removed) to the RCA outs, between the ground leads (where green and blue cartridge wires go, or the grounding shell of the RCA cables). No cross talk issues with the live leads. Before I go mucking around with solder to remove the tone arm wires and the RCA cables to test which of those is the issue, can anyone confirm whether cross talk between the grounds is actually a problem and would be what is causing my left channel to go out?
I looked at the connection where the tonearm wires and the RCA cables connect inside the turntable and I can't visibly see any issues with the current soldering job and no visible wires are crossed between the two. Obviously I'm without any actual electrical engineering knowledge, but it just seems odd to me that the two grounds would (a) be connecting somewhere, and (b) that that would cause my left channel specifically to go out.