My AC is cooling OK, after I spent $250 last week having a new blower motor put in the furnace unit, but it continues to make a "knocking" sounds for a minute or two after the fan shuts off. It's so loud it wakes me up, which is why I'm posting at 5:20 A.M.; I also noticed that the line is icing up.

Icing around the evaporation coil is often caused by dust and dirt buildup on the coil. This comes about by not changing the filter frequently enough. If you decide this makes sense, have a professional check it out. It's usually not a job for a do-it-yourselfer.