The PS-1F is rated for 4 beltpacks. My guess is that you've overdriven the
power supply and a component inside of it like a
capacitor has blown up. Unlike the larger
power supplies that detect an overload and shut down to protect it until the fault is cleared, I expect the PS-1F might just keep plowing along until it overheats and starts wigging out.
The first thing I would check -- ONLY with the
power disconnected to the
unit, is to open it up and visually inspect the components. Should be pretty obvious from smell or sight if something is scorched. If so, it shouldn't be hard to fix but would prove the
system's been operating with too many devices attached to it and that it's time to upgrade to a larger
power supply.
My second inclination is that if swapping the
power source reliably removes the problem, you may have a short to
ground somewhere. I would pull open any/all wall plates you have intercom jacks at and visually inspect that none of the shields on the cabling have become shorted to the
conduit or
back box. Could be a
wire was stripped back too far or during a
wire pull a
wire was dragged over a
conduit end and the cable
jacket got nicked. In this case, it could just be that in the time it took you to troubleshoot and swap
power sources, the
power supply cooled down a little and it wasn't actually the source of
power that was causing the noise.
