Yes I am going to definitely take a look at power supply, I have mainly had the complaint at 1 site on station 204 which is on backplane, the other is 210 at another site, but both are similar complaints, the 204 cannot hear the noise but outside callers and intercom callers do, we have replaced wire & keyset . The auto attendant is actually 1 we are calling into , but it will not respond to our dtmf tones. We have replaced a bunch of the 100 power supplies, so the 1st problem could be that?