Its not a hum like a ground loop hum. Its is more like crackling, like the sound you hear when welding. Speaking with Valcom the OEM, they state shielding the speaker run is not necessary. We all know that the OEM does not always no best, so it might be worth a try to shield the cable. This system has been up and running since 2001. Just last year 2011, no building change, this noise starts. I would like nothing better then to start throwing breakers. My issue is the breakers I need to throw, control our computer systems and offices. The second issue with throwing breakers, this noise is so erratic that we can hear the noise only once a day. Maybe the next day 4 times, maybe 30 times in one day. This noise follows no suit so I cant relay it back to any type of AC that would start and stop like that.
