Have seen this voltage on ground problem many times with catv. Most times it has turned out to be a bad underground neutral. Had an entire street all underground fed with the cable drops melting due to this. Power company had to send out " power quality " troublshooters to find the problem and sometimes it takes several visits and can be a real pain because these problems like to be intermittant. Sometimes you will see voltage issues when you do a load test. Good luck
