Weird popup on screen
MacBook, iOS 10.1
It looks like a broken variant of the volume/brightness overlay you see when you increase / decrease those settings.
Does it display immediately after each reboot of the Mac?
I would try booting into safe mode to see if the problem is reproduced there to. To try this:
1- Restart the Mac.
2- Press and hold the Shift key until you see the login window.
3- Enter you login details as usual.
If the broken overlay/popup isn't showing while in safe mode, this may indicate you have some incompatible software installed on your Mac causing the problem.
It's also possible that simply rebooting the mac (normally this time) will resolve the issue, as booting into safe mode clears system caches among other things that may have become corrupted over time.
Failing this, try resetting your macs PRAM. Instructions here:
https://support.apple.com/en-gb/HT204063
Also try resetting the SMC:
Re-booted & so far so problem! Thanks a lot!!!
It appears to be a botched display of the volume popup that appears when you increase/decrease/mute/unmute the sound.
Thanks!
Weird popup on screen