Udev net issues

[Joseph L. Casale]

In trying to swap a motherboard for the exact same type I kept having issues
with the NIC not being started (network manager was disabled). I finally found
70-persistent-net.rules under udev had the mac address of the old nic as eth0
so I moved this file out and rebooted only to see it was recreated as expected
but had the old mac address? I finally edited the mac address and that worked.

Where in the world would it have gotten the old mac from?

Thanks,
jlc