Mine have now done about 26,000km (16,000miles). The only noise is an occaisional "twang". I'm hoping it's just stones getting stuck in the spring.
The bottom coils are getting chewed up from stones and rusting a bit. I wish I had got coil wrap.
I recently adjusted the bottom mount for minimum camber and the top for maximum camber and got -1.8deg while messing around learning to do my own alignments. This allows alot of water,dirt and stones up through gaps in the top mount so I will readjust the bottom mounts back to max negative and pull the tops back out to stop the mess and get a bit more camber.
Started doing my own alignments using fishing line, a sinker, digital calipers, jackstands and a scienific calculator. Use a bucket of water and some clear hose to find the slope on the floor and adjust the measurements. Only 0.2 deg down to the left for my spot, so add 0.2 for the left camber and subtract 0.2 for the right. Close enough for now. Later I might get tricky and make up turn plates etc.
So far, BC still has my recommendation from a daily driver/weekend canyon carver point of view.