Beringer Xenyx 1204fx emits a clicking sound... Sounds like a Geiger Counter for radiation in my headphones. I have used the same sound mixer in the same configurations for 3 weeks. Now I've had it running for a week and no problems till this morning. I've disconnected all inputs and outputs and still get the clicking in the headphone jack.

This is likely a problem with the FX in the unit or the power to it. Does the FX display act correctly? Check that the headphone source "Main Mix" is the ONLY button down for the headphones. If not, make it so. If the clicking is still there, try the headphones in the aux send jacks... see if EITHER left or right can hear the clicking. Back in the phone jack, scan across the SOLO channel buttons down one at a time. Is there clicking? If not, the problem involves the mixing buss or further down the line. Make sure the SOLO buttons at the FX Aux sends are up.
What effect does the MODE button have in SOLO and in PFL? Is the SOLO LED off? Is the number in the FX window SOLIDLY on and not flashing?

My 1204fx effects do not seem to make it to the output stage of the mains plus 7/8 clip light stays on