The noise or clunk noise may be the floor brush. Here are two possible reasons:
1. The floor brush may have debris stuck in it, cleaning the floor brush thoroughly.
2. The roller brush inside the floor brush or other parts may be deformed and need to be replaced, email at official@ibuture.com with pictures or videos of the issue to arrange a replacement (only for those orders are during the warranty)
(Brushes Order Link: Click Link)