This summer our air conditioner starting rattling.
I know of no other word to use to describe the noise.
It was an intermittent noise but very annoying. It also seemed louder at night, when we were trying to sleep. We tried changing the temperature setting and it still rattled. We changed the filter, it still rattled. Since I know nothing about air conditioners, I could think of nothing else to do but call for help. We finally put in a call to our landlord and she promptly had an HVAC technician come out to inspect the problem. Of course the air conditioner was not making noise when he arrived, but after a few minutes he understood our frustration. He completed a thorough inspection of the HVAC system, inside and outside the house, and determined that the coils were not defrosting. He actually showed me the thick layer of ice on the coils. The HVAC technician said we needed to shut the air conditioner unit off for a couple of hours to allow it to defrost. The technician cleaned the air conditioner unit inside the house and recharged the refrigerant. He said we should be good for a little while. The HVAC technician then said the air conditioner was over 15 years old and on its last leg, it really needed replacing. Our landlord had just purchased this unit and remodeled and made extensive repairs. She really did not want the expense of replacing the HVAC unit at this time. I could totally understand that! Defrosting the air conditioner coils and adding additional freon did get us through the summer without any additional problems.