Upon arrival, the customers complaint was the system intermittently making a slight knocking noise. When I arrived, the system was on and running. The customer said it’s cooling fine. It just makes a noise every now and then. I had the customer turn the system off. I got in the attic to the air handler where he says the noise is coming from. I had turned the system back on everything came on and was running good and looked as good as it could for the age of the system. I will do a follow up in a week or so just to see if the customer is still hearing the noise.