Metal Detecting

Towards the end of todays hunt the headphones (I have the full version) went very faint and tinny, both sides were working, but even on full volume they were a poor act on what they have been previously. Scanning the coil over a coke can should have given a banging signal but all I got was some half hearted beeps. I've had this intermittently before but cured itself by turning the phones on and off, though this time that didnt work.
Does anyone have any ideas as to the cause?

Not heard of that before John....? sorry

I had issues with my WS5's , the sound was faint , then went loud in one ear only , I sent them back to crawfords who said it was a common fault , they changed the cable across the head band ( under warranty ) they have been fine ever since