2003 Cadillac CTS Minoe noise from engine

Any noise is two things that don't get along mechanically, physically, even emotionally(arguement). The louder, the worse, if you hear and feel noise, check it or have it serviced. If you just hear it only once in a while, I would wait until it gets loud and steady and easier to check and repair. But that is only my choice. A belt sometimes makes the oddest sounds. Spray silicone and see if it goes away or changes. Your welcome.