Yea. Double check the wiring on the cart, make sure none are loose, check if it all looks clean (if not use some contact cleaner). I guess in built pre amp also means no separate ground wire? Any way to bypass the pre amp on that model?
Btw it's probably not this but carts can pick up EM inference, have you put anything near it that didn't used to be there, like your collection of healing crystals or magic noel edmunds anti-cancer machine?