Over the last 6 months we have noticed that the AC compressor on our Gen 3 - 2012 Prius III is getting a bit loud. It still cools great but it has a clackity clack sound. My question is, what's normal? The sound goes away when we turn off the AC system. I've had 2 other Gen 3's that didn't have this noise but from what I understand the AC compressor can be noisy. Since this is a variable speed electric scroll compressor is there any reason to change it early to keep from burning up the inside freon and putting metal shavings in the system or will it simply stop working when it goes out?