@tgimagine
Make sure no one has plugged the same cable into 2 ports on the switch or under a desk, try unplugging about half your computers/printers and see if the problem remains. If yes, plug the first half back in and unplug the second. APs, too. Process of elimination.
Also, on the off chance it is the SG, take it off the net. Maybe bad NIC out of box.