It would seem more like metal to metal contact would make that noise. Maybe there isn't grease where there should be grease, or maybe something was damaged in the replacement process??? I think you should dig into it deeper and see if you can find anything suspicious. Maybe even see if there's actually CV grease in both CV joints, and then put new hose clamps on the boots to replace the factory clamps. Verify that the orientation of the dust shields at both ends is correct and nothing is scraping against them. I assume you have the more common permanent hubs, not manual hubs, right? Did you use a torque wrench during reassembly?