Macbook Pro i7 - 3 beeps on startup?

My Macbook Pro battery had run down (it does quite a bit) so I rebooted with the power inserted.

I get a frozen screen saver which is normal, while the progress bar finds it feet back on power.

However this time, I had the frozen screen saver, and a continuous 3 beeps which I've never had before in a loop? I then re-pressed the power switch on the Macbook and it rebooted fine and seems ok.

Do I need to worry? This i7 is coming up to its first year (which I think is covered by Apple?) and I *think* this maybe a memory issue?

If it is, and my Mac is covered, then by a sheer stroke of luck, I decided to get Apple to fit the 8GB memory at the time of purchase (bad I know! and I don't usually do that) BUT that would mean that Apple fitted the memory upgrade and I haven't touched anything myself.

Can anyone clarify if these 3 beeps are a dying Macbook? memory issue? nothing to worry about?

I then booted up this morning with a full battery and the boot up took a lot longer than normal - maybe around 3 minutes on the spinning logo, and then finally booted - are these all worrying signs?