Sudden loss of volume from turntable


Hello all. My system has developed a problem where the volume from my turntable disappears suddenly while an album is playing. This has happened a couple of times after using turntable for an hour or so. I have a modded Tecnics and Denon cartridge, into a SUT, into a pre amp phono stage. CD through the preamp functions without issue.
So maybe an issue with cartridge, tonearm wire, SUT, or phono stage on pre. Need help, were do I begin? Thanks
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Thanks I will try those suggestions out, very much appreciated.
Can it be the cartridge?
Could be the cartridge or the wires or clips........but it would be unusual to then affect BOTH channels?
I have a similar problem (total dropout of one channel or the other) and I'm pretty sure it's the ancient wires from the TT to the phono pre-amp. Will be replacing as soon as I get the wherewithal to do it (some soldering required on mine).