Unlike the first time, I never found anything I could see, but this seemed to fix it for me. Try cleaning out the problem socket with a small, stiff, clean paintbrush. Does the beeping come back? It may be fine for some while depending on how long you have been on battery power. 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.Ĭheck the plug looks clean. However, there were some clues that pointed to something connected with the power. On each try take a look at the system configuration and see if it is reading correctly. Try it in one slot and then the other slot. MacBook Pro 13 inch mid 2010 Processor 2. To test use just one stick of RAM and remove the other. However, recently I have seen three 2011-2012 machines where it is not and is the logic board. My current macBook-Pro does not have a magnetic power cable. The three beeps has historically been a RAM issue. I eventually traced the problem to a small metallic fragment that had got stuck in the magnetic socket. This was doing roughly the same thing, and the reset commands were not helping. I had an old MacBook-Pro with the magnetic power plug.

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

Macbook pro 3 beeps when starting