I checked, and some of the screws in the bottom panel were loose.

I googled the problem and it says 'bad RAM' basically.

I was just sitting on the couch with the computer leaning slightly to the left on my leg. Moving it while holding it by the very edges with two hands does not cause the problem, so I figured, 'OK, just don't lift it with one hand, and I'll be OK.' Didn't have anymore issues until just now.

Second time it happened, once again I was moving it while pushing on the left underside due to just holding it with one hand. But I was in the middle of a presentation and had no time to diagnose. So my fingers were pressing up on the underside of the computer. In that instance I was only holding it with one hand, my left hand. The first time I had picked up the computer and was moving it across the room while turned on - not usually the best idea, I know, but in the 10 years I have owned Apple notebooks, I have never had my computer freeze from being lifted or moved before. Three different occasions I have been using my MacBook Pro, then had it freeze on me with three beeps.

Macbook pro 3 beeps loosen up screws