I have a 1999 Suburban. 5.7 engine. 130,000 miles. I have owned truck for 6 years. Never had an issue with AC, always ice cold. Last week the compressor started cycling on/off, and air was not cold. I went to parts store and bought DIY freon kit, with gauge. Filled to 35 psi. Now ice cold air. Compressor remains engaged. No leaks that I can see, and all good after a week of driving. But... I notice a very slight clicking or very low knocking sound coming from the compressor. It do not hear the sound until the engine reaches full operating temp. The sound can only be heard at idle and does not increase with RPMs. I can't hear the sound inside the truck, or while driving. I only hear it when standing in front or side of truck. I will be taking a 1200 mile trip to South FL next week. Is this something I should be concerned about? Any thoughts on trouble shooting? Edit: I forgot to mention... Right after I added the new freon, I also changed the idler pulley, tension pulley and new belt, due to worn noisy pulleys. It was only after everything quieted down, I first heard the AC ping noise. So I do not know how long this has been going on. Thsnk you, Shane.