Had a customer call me today and tell me that one of the Adtran TA750's I sold him is making a cracklin' noise. I had him disable the ringer circuit (poke the little button) and the noise went away.

The channel bank is still working, but obviously this shouldn't be normal.

Other then replacing the card with a new one, is there anything to be looked at or repair'd on the old one? Is it even worth messing with?