I have the exact same thing with my IPhone 7 Plus. I noticed it yesterday after updating the IOS to 10.2. I think thats a coincidence because it looks like a hardware problem - loose part etc. However I've also noticed "clicking" sounds from the top speaker near facetime camera. Seems very strange, especially that it happens not too often. I can, however, reproduce the noise while clicking the home button rapidly for 10-20 seconds.
Have you managed to fix it? I've been to a Premium reseller Service point but they asked me to leave the phone for ~2 weeks which I cant do. Besides they said that it looks like a minor "discomfort" and would probably do nothing. I was expecting more....
I will try to record the problem and put it on YouTube.
Oh, and restarting the phone as somebody mentioned didnt help at all.