Awhile back, a customer of ours experiencing a similar issue, determined the noise was present on the ceiling grid and being induced into the speaker. This noise was constant, however and each time the ceiling speaker was lifted above the grid, the noise stopped. The customer ended up placing rubber or plastic tabs at each of the 4 corners to provide slight separation from the grid. Again, grasping at straws.
Definitely agree with other members here that have stated the noise is from an external source and not that of the paging system.
