Two of my three Multy X's loses connection and starts to make noise

I have just installed three Multi X's in my home. Installation went fine, and everything was working just fine. Now all of a sudden after a day or two the two satellite Multy's are starting to lose connection to the primary Multy, and making a hiss noise. I have to restart them all three every time that happens, which is daily, in order to get back online.