Isn't a bad ac compressor supposed to make a noise all the time?

A bad AC compressor can make noise, but it doesn't always do so consistently. It may produce loud clunking, grinding, or hissing sounds when it's struggling or failing, but it might also operate quietly at times, depending on the nature of the issue. If you hear unusual noises intermittently, it's a good idea to have it inspected, as it could indicate a problem that may worsen over time.