Panasonic model KX-TG5571

I the a 5.8ghz phone at my home. It's a Panasonic with an extra handset. When using the phone the person who I am talking to tells me that my vioce fades in and out. I have had Ma bell come and check the lines, they left without saying good or bad. I bought a cheap corded phone for test purposes and plgged it in outside. All seems well. The coreded phone works good inside but there is a little hum on the line. I also have a 2.4 ghz phone which seems to work ok. I have spoken to Panasonic who said to remove batteries and let sit for 2 mins then reinstall and try again. In the mean time I spoke to a neighbor who is also having trouble with a 5.8 ghz phone. Does anyone have anything to say regarding the 5.8 ghz system?