There used to be, a couple of months ago you weren't allowed to perform more than 12 actions (posts, comments, downvotes, maybe reports?) every 5 minutes.

It seems to be gone though, at least, for me. I made a new thread, deleted it and was able to post 50 comments in under a minute.

I don't think it's a feature that would have been removed on purpose. My guess is a recent update broke it and noone's been able to fix it yet.