It sounds as if the 1/4" jack has become faulty. The only other thing would be a cord with a break in the interior wire, causing and intermittent connection and signal transfer. I have had this happen with repeated stage use. I tested the cord with an ohm meter attached to each end of the cord wire and starded bending the cord, going from one end to the other. Mine was broke about 4" from one end and would loose signal with the slightest motion. I cut the cable about 6" past that point and re-soldered the wire and still use the fixed cable. Good Luck