It sounds like you've got the "creeps", we had a lot of freeze/thaw days around Christmas, you're weather was probably about the same. If your dirt covering expands/contracts a smidge, the trap fires. (above you said the pan was free falling)
Let me ask about your baseplate. All my SC 1 3/4's came with a center swiveled chain, did you remove that center-swivel setup?, and how did you weld your baseplates on? It's possible you got enough heat on the springs to ruin them. My S.C. traps are about the same as they were when I took them from box.