Unreliable facebook messenger sound

For about a couple of months now, my facebook messenger notification sound has changed. I usually use the default sound and have never had a problem but now I sometimes get that sound and sometimes get a very soft click that I will only hear if I’m within about a metre of the phone. It doesn’t matter if I’m in a chat, simply have messenger open, or messenger is not in focus or even closed—the issue comes and goes so that I cannot rely on the notification sound to alert me to incoming messages.

I keep my F4 up-to-date, including the apps. I’ve read and attempted the numerous fixes offered online (including deleting messenger cache/storage and uninstalling/reinstalling messenger) without success.

Any ideas?

Regards,

Mark