One beep occurs when I update my Mac

The following table lists the new tones and their meaning:

Tone(s) Description

1 tone, a 5-second pause, repeat No RAM installed

3 successive tones, a 5-second pause, 3 successive tones RAM does not pass data integrity check

1 long tone when holding down the power button Firmware upgrade in process. See About firmware updates for Intel-based Macs for more details.

3 long tones, 3 short tones, 3 long tones Firmware restoration from CD in process. See About the Firmware Restoration CD (Intel-based Macs) for more details.

http://support.apple.com/kb/HT2538

Older meanings...

Can you count the beeps or flashes?

1 beep = no RAM installed

2 beeps = incompatible RAM types

3 beeps = no good banks

4 beeps = no good boot images in the boot ROM (and/or bad sys config block)

5 beeps = processor is not usable

In addition to the beeps, on some computers the power LED will flash a corresponding number of times plus one. The LED will repeat the sequence after approximately a 5-second pause. The tones are only played once.

Note: In this case, a flash is considered to be 1/4 second or 250 ms or greater in length.

http://support.apple.com/kb/HT1547

The power on self-test resides in the ROM of the computer. This test runs whenever the computer is turned on after being fully shut down (the power-on self-test does not run if the computer is only restarted).

If a fault is detected during the test, you will not hear a normal startup chime. Instead, the system will beep as explained below. If you experience one of these beeps, you may call your Apple Authorized Service Provider for additional troubleshooting assistance.

1 beep = no RAM installed

2 beeps = incompatible RAM types

3 beeps = no good banks

4 beeps = no good boot images in the boot ROM (and/or bad sys config block)

5 beeps = processor is not usable

In addition to the beeps, on some computers the power LED will flash a corresponding number of times plus one. The LED will repeat the sequence after approximately a 5-second pause. The tones are only played once.

Try one stick of RAM at a time in each slot.

One long tone used to indicate a system firmware update was being initiated. If the firmware update is not able to complete, then you may need to use a firmware restoration CD, but I could not find any version that is compatible with your 2010 iMac. If the firmware update cannot complete and there is no firmware restoration CD, then try an SMC Reset, otherwise your iMac is a brick (assuming the tone indicates a firmware update and not a memory failure) since it is not economical to replace the Logic Board plus you must be extremely careful a replacement board is not locked or controlled/managed by the previous owner.

One beep every five seconds

Your Mac isn't detecting any memory (RAM). If you've recently added or replaced memory, make sure it's installed correctly.

OK, I think it was the Firmware Update tone. :)