The Rear springs on these vans are sometimes problematic , the top adjuster on that kit isnt well designed and can move around on the chassis welds you can see a thin rubber washer that they use in an attempt to stop it ! the lower coils are designed like that , and they so make noises hence the rubber tube they fit around the coil once again to try and stop noises , the rubber can wear through .
Changing them to a better design might be a way to go as those springs are notorious for breaking .