My MacBook Pro beeps at random intervals

Question

I was awakened last night by my MacBook beeping at what seemed like regular intervals. I shut it down. This morning I turned it on and the beeping came back. It was not completely regular. Sometimes, after restarting, with or without one of the many magic key sequences to reset something, it would be okay for a while.

Just before the beep, I noticed the screen dimmed briefly. There is a preferences option to dim the screen like this when going to battery power. I noticed the battery had not charged beyond 80%. There is an Optimised battery charging option in the Preferences. It wasn't ticked, but it says "To reduce battery ageing, your Mac learns from your daily charging routine so it can wait to finish charging past 80% until you need to use it on battery."

Answer 1

This solution may not cover all cases, but I have seen it twice. I am writing my solution here, so I can find it again if it happens a third time.

I had an old MacBook-Pro with the magnetic power plug. This was doing roughly the same thing, and the reset commands were not helping. Someone suggested a faulty power supply. It was not that. I eventually traced the problem to a small metallic fragment that had got stuck in the magnetic socket.

My current macBook-Pro does not have a magnetic power cable. I am using the original charger. However, there were some clues that pointed to something connected with the power. If you are seeing a similar problem...

Unplug the power supply. Does the beeping stop? If the computer is thinking it is swapping from the power supply to the battery and back again, this ought to fix it in one state.

Check the plug looks clean. Plug it into another socket. Does the beeping come back? It may be fine for some while depending on how long you have been on battery power. But this seemed to fix it for me.

Try cleaning out the problem socket with a small, stiff, clean paintbrush. Unlike the first time, I never found anything I could see, but this seemed to fix it for me.