I realize this is an old post, but I had a similar problem with my iphone7 lately. I tried shutting the phone off and back on, but nothing happened. I went to settings to turn off vibration as the rattling noise was extremely annoying. Surprisingly, it just took me to change the vibration from the default tone to something else then back and voila..the problem is gone.
I am not sure if this will work for everyone but I thought of dropping this here in case it helps.