Freeze and 3 Beeps, Late-2011 Macbook Pro

Whenever my computer starts to heat up (if I have a few tasks running simultaneously or HD video playing), the screen becomes scrambled and I hear 3 beeps, which repeat after about a second or two delay.

Based on my research, this is probably an issue with my RAM, but I haven't seen anyone mention a case in which their computer was otherwise fine, only not working when it gets hot. Others have reported that their computers won't even start.

What I'd like to know is, how can I check my RAM? And does this sound like a case in which I just need to take out and put in the same RAM (that there's a connectivity issue) or will I have to buy new RAM to replace the current?

Your help would be appreciated. Thanks in advance!