We had our AC2102XE0 unit running, and it began a loud screeching noise, almost like an engine noise. We turned it off. How do I check if I need to replace parts, what I will need, etc. At times in the past month, it will randomly sound like a chunk of something is falling or rattling around in the unit. Additionally, in starting it up for the summer, occasionally it would shoot out little black specs - if that helps diagnose the problem that has reached this screeching halt.