notification sound repeat multiple times when receiving an iMessage

Over the past 6 months or so I have been getting multiple sound notifications when I receive an iMessage. It happens randomly and sometimes can result in 3-4 notification sounds when just one message is being received (almost like an echo). Occasionally when it happens it will do a lot of multiple 'pings' with a random variable gap between them and on a few of the 'echos' the sound is truncated.
I use the 'Ping' sound as the notification, so it'll cut off part of the ping sound on a few of the echos, so it sounds like this:

Ping....ing......pin..............ping ping ping ping ping .... ing.. ing.......pin.g....g...g...gg

Like a weird bouncing random echo which cuts off parts of the sound randomly too. There are sometimes 15 to 20 'echos', most often it's between 2 - 4. It only happens every so often and it happens when only one message is being received.