Ok, I installed a partner acs 509 approx 1 yr ago. the system consists of a 509 with (2) 308ec cards in a five slot carrier. Om the original install date all system functions were tested good including over head paging. About a mth ago they started to get a loud squeal whenever they would page from a single line phone. tired new phones, squeal.. tried new page port, squeal... new processor, new five slot, new speaker, nothing is resolving this issue...I've narrowed this down to a slt plugged directly into system and a single new speaker directly into page port...all slt phones squeal when the hook switch is depressed...please help with this squeal