loud alarm sound

Just a few moments ago, my MBP (early 2011 model) made a loud alarm like noise and the light on the lower right of the laptop was flashing. After I lifted up the bottom end of the laptop and it lightly came back down on the table. I was downloading images and backing up to my external harddrive when this happened. The laptop froze while the alarm sound and flashing light continued. Very bizarre!!

As the laptop was frozen, I did a forced restart and the laptop rebooted up fine.

Recently, I was at the Apple Store to get one of the rubber bumpers replaced and understand that the back cover had to be taken off to complete this.

Don't know if something could have happened from this, etc?

Curious if anyone has experienced this alarm sound/flashing light scenario by accidently lifting and placing the laptop in any abrupt manner.

A quick diagnostic was recently done on the laptop and everything shouldn't up fine.

any thoughts.. Atcandela