Darn I was hoping someone would have an answer for you. My rear air conditioner/heat pump (Dometic) rattles loud enough that we can't sleep with it on. Since we should still be under warranty mine will be going back to the dealer for this soon. I did read somewhere that the aluminum insulation tape in the ducts sometimes comes loose and makes noise but I don't think that is my problem unless it is hitting the fan.
Brian, Loretta & Daisy (Golden Retriever)
2008 Holiday Rambler Endeavor 40 PDQ , ISL 400
2014 Ford Explorer toad