I have an old (20 yrs or more) Nutone system in my house, I moved in 3 years ago, never used the intercom feature but liked having music all over the house. The Nutone worked great for about 2 years but a year ago the master unit started to make a loud buzzing sound and I haven't used it since. The sound can be geard in each of the speakers in the other rooms, so I just had to shut off the main unit. Has anyone figured out what is causing this and how to fix it?