Got a customer with an ACS R6 with 18D sets. Loud squeal starts when adding a line for conference. 1 - talking on first line; 2 - press Conf and dial second party; 3 - Press Conf to establish conference and loud squeal starts.
I have never seen this, but I suspect high loop current. A friend has borrowed my VOM so I couldn't test loop current, but have any of you encountered this before? I will return tomorrow with VOM.

Yes it is comming from the lines, they make a 90A Attenuator that will cure it. You will need one for each line that has the problem.

Could not locate any 90a attenuators, so I purchased some current regulators from Sandman. I am still getting the squeal when a conference is established. Lines have 40ma without regulators and 25ma with regulators. Otherwise, lines are clear.
Any more suggestions?