Whats on your turntable tonight?

Very wound up right now, need to take some deep breaths.
Fired up the Rega mono rig and very loud background hum had appeared.
Tried all sorts of grounding tricks but to no avail.
Then I figured the only thing I had done since last played was swap the tonearm cables over between the two tt.
Should NOT have made any difference but swapped them back and peace was restored.

WTF!!!!!

@uberwaltz
One cable has an incomplete ground connection. It is not important for some reason on one tonearm but the other, well hearing is believing...

Mark Knopfler - “Tracker”

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Drrsutliff.
now I have regained some composure you are likely correct.
I believe it is the cable that came with the 401 as once that was on the Rega is when the hum was very noticeable.
Even back on the 401 it is louder than I would really like.
The slightly to short cable that came with the Rega is very quiet back on the Rega.
Solution?
Open up the 5 pin din end of the offending tonearm cable?