Hi Ray,

I had this happen some time ago when using 'phones on my KN7000. It turned out to be just some deposit on the 'phones Plug or KN7000 Jack Socket.......
Try applying a little switch cleaner solution on the 'phones plug, insert the plug in your keyboard and rotate the plug a number of times to dislodge any 'muck' on the socket connections. Worth a try.............
Sometimes a deposit can be present on these connections and you can't see it, and it doesn't take much to make this type of connection fail - they are often only point contacts between the plug and socket.