When you enable Rampant's "World: Enable new enemies" option, and you have "Enable artifacts from aliens" disabled, biters will start dropping artifacts again, regardless if you toggle the setting on or off. Not sure which mod is at fault so I thought I would start here.

If you turn off "Enable artifacts", they don't exist, my mod doesn't create them.
if you turn off "Artifacts from aliens" (name might be different, I'm not looking at the locale entry), then my mod just doesn't add them to the drop tails of biters and spitters, but are still dropped from nests and worms.

If you have the first case and they still exist, or if you have the second case, but they're still being dropped by aliens, then it's Rampant causing the issue.