i took out a old nec professional system and replaced with nortel cics. next day they got a loud squeal out of the page horn. bogen amp. they wernt doing a page it just started squealing. i came out and it did it again. this time when a call was ringing in. i called the company we got it from and they insist it isnt the ksu but the amp. it worked fine with the nec system. anyone have an idea on this. they have two horns. thanks. dave