Well we had a similar issue a couple years back. We triangulated the source of the noise and then had someone look up various pager transmitter licensees in the general area. Then it was a matter of getting near each site and listening and seeing what happened. Managed to narrow it to a hospital and when they were told what happened (it was jamming repeaters for at least 3 counties!) they quickly called to get it fixed. (Something about notifying the FCC of a problem may have helped too.