What could a loud beep upon startup mean on my computer?

not beeps, or beeping, just one loud beep. Louder than what the speaker is on. I've heard it probably 3 separate times now, usually when it starts up, but everything seems fine. one time, it was on standby, and it did it. I'll be monitoring it close now. Thanks.

but it doesn't do it everytime...that's why I was/am confused.

ok...whenever a computer beeps during the boot sequence it is because it is doing what is called a POST test...you would need to consult your motherboard manual to figure out what the beep means...your manual should have a section that says one beep = ??? and two beeps = ??? etc.

It's a good beep... It means your cpu is working and your system is posting, getting ready to boot. if you dont like the beeps, look for the internal speaker in your computer case, and unplug it from the motherboard...its not needed unless you need to hear the different beeps.

Laptop? Maybe battery alarm?

Knowing if it is a laptop or desktop would have helped. It could be a low battery warning for the CMOS or BIOS or a laptop it could mean a bad or low battery.
Generally most computers will give one beep meaning all systems check out and are good to go at start up. You may read the motherboard manual or the manual that came with the computer and see if there is any indication what the beep is. Most motherboard manufacturers let you know what the "beeps" are.