Creaking C Pillar

So my mom has a 05 X5. Lately a noise has started up and I'm just plain tired of it. It's extremely loud when going down the road. You can only hear it when there's a bump or rough pavement. It isn't as bad when you take out the rear roll up sun shade though. I've tried tightening up screws, placing foam, etc. So I come to you Bimmerfest, help me fix this!