There is a musty odor coming from two of my AC vents in my living room which are located in the ceiling of my home. I have a very old (10+yrs old) Central AC unit and compressor. I haven't turned it on yet this season. The only thing Iíve done directly related to my AC unit is remove the protective cover from my compressor that I apply every winter. What could be causing this odor?

Thanks in advance