My mac still makes 3 beeps but the RAM is ok

I have a Macbook Pro (From Sept 2011) and 3 days ago, I put a CD in my computer to watch a move and then it froze and made the 3 beeps and this is the first time that has ever happend. I shut it down then put it back on and it was fine. The next day, my labtop was fine all day but then around 7pm, it made that beeping noise again and my computer wouldn't turn on. I finally magaged to turn it on. The day after that I took it to the Apple store and they ran some test on it, checked the RAM, put it back in place and all. When I got it back it wouldn't boot. The guy took it back to run addition tests on it. He told me to come back Friday so I could save all my info because he might do something that could wipe out my memory. At the moment, my computer works. But at random times, espically when I'm on sites like Youtube, it will make a crackling sound and start the beeps again. I power it off, then turn it back on and it's fine but it keeps happening. In the meantime, before I go back to Apple, does anyone know what the problem might be if it's not the RAM even though the 3 beeps do indicate no good banks?