catalyic seems fine can the noise be from belts?

[kalaydjian]

I went under and hit the cats no rattling, I checked the ebpv valve by moving it it did not rattle also started the car went under and looked at the ebpv the car started at 2000 rpm for about 3 minutes then I saw the valve move to the right and the rpm went to 1000 I assume that is the open position on the ebpv to the right, can that rattle noise be comming from my belts, you hear it more when the car is cold than when it is warm up, belts also sometimes make a skreeching noise when I give it gas on neutral at 4500 rpm, any ideas thanks again. Alain