Last Summer, when I happened to be mowing the lawn or doing other yard work, I began to notice that my exterior A/C unit was making some sort of strange rattling noise when it was running. It was not such a loud and violent noise that I thought I needed to call an HVAC specialist immediately, and I actually ignored it for a few weeks. One Saturday however, after I came inside from trimming the hedges, I decided to take a shower, grab a drink, and sit down at my computer to research what might be causing the noise on the internet. Turns out there were several possibilities as to what was causing the racket. Lawn care can get messy, and the first possibility that caught my eye was that some sort of debris such as leaves and sticks could have fallen into the unit and might be causing the rattling. I figured that was probably it, but I read about other possibilities. Another very simple explanation was that there were some screws or bolts loose somewhere in the machine that were vibrating. I figured that was an easy fix. A third possibility had me a little worried though. The rattling may actually be the compressor. It seems that the motor on older models will gradually make more and more noise as time goes on, which could be a sign of the compressor nearing it’s point of failure.That was an undesirable proposition, so I finally decided that this problem warranted a call to my local HVAC service. I made an appointment for the following day. I was quite relieved when the HVAC repairman quickly discovered that the problem was indeed nothing more than an excess of lawn debris getting into the system and causing the rattling noise. He was able to clean it out lickety-split. Still, the repairman agreed that I made the right decision in calling him about the problem as it could indeed have been something more serious, like the compressor. I enrolled in an annual maintenance plan, so that I can have someone come out and address similar problems in the future.