We have an Avaya IP Office 500 system. We have three VOIP lines from our cable internet provider Suddenlink. Several times a day our calls sound like a cell phone call cutting in and out and then the call drops. We've patched these lines directly to a phone and the problem goes away. Our Installer has been out several times and can't seem to resolve the issue. They've even went as far as replacing the entire phone system. Is there some setting in the phone system that could be causing this? Thanks for any suggestions.