I have an audio system installed in a school auditorium that has multiple mic's (wired and wireless) as well as DVD,CD recorder/player, and a Multi-media projector mounted at the rear of the stage (rear-projection).
The problem (Mexican Radio) occurs when the projector is shut down/turned off. The projector then goes into "cool down" mode...this is when a local radio station 1440AM/102.5FM comes through the projector channel. Once the projector finishes cooling down and totally shuts off the radio station audio fades out. We have changed out projector makes and manufacturer and it still happens. We have tried both balanced and unbalanced. We have changed the input channel on the Ashly NE 24.24M w/FR-16 network remote...and still have the issue.
We have narrowed it down to what we believe is a Power issue. The auditorium is 61 years old (in its current form) The auditorium was actually built in 1933 but suffered a fire in 1951. The power to the school is very susceptible to spikes and surges and is also very "Noisy" according to the maintenance staff the power was destroying computers and the like. They do have fairly recently installed "Isolated Ground Receptacles" of which the projector is plugged into. We did also plug the projector into other non isolated ground receptacles and the radio audio also came through...in addition the non isolated ground receptacles added enormous amounts of hum/noise.
We are contemplating putting power conditioners on the amp rack, mixer, and the projector and wonder if that would alleviate the problem. Looking for help!