Yes. The floor storage panel. Apparently it can shift around freely. On the other forum (that I am not allowed to mention here) the guy posed a video illustrating the source of the noise. If you search F150 lightning forums on Google it will be in one of the first links. You can search the...
In another forum I was reading that some people are hearing an audible clunk from the plastic divider in the frunk. Not saying that this is your clunk but it does track with stopping and starting. https://www.[banned site]/threads/clunk-in-the-frunk.1260/#post-12162