I think we are talking about 2 different issues. Can you create a video and post it here?
The quote below is the best description to what I am experiencing. It is an intermittent issue, and I have heard it on my GF's 7+ too. I am hearing this anomaly during some iMessage notifications Not sure how I would create a video... Recording the screen? If so, it would be very hard as the problem is intermittent.
Define "stuttery"?
11.3.1 is fine on my 7 with one exception..... notification tones sometimes play what I would describe as jerky or "stuttery". Like portions of the sound repeat several times randomly before it moves on to the next portion of the sound. Is that what you mean??
Paul