MacBook freezes with three beeps My Feb-2011 MacBook Pro hangs with three beeps.

I noted the first strange thing a few days ago. The MacBook was in standby (as always) but very hot (not usual). I thought some process must have stopped the mac from switching to stand by and kept the processor busy, so no big deal.

Switched off, booted up normally. After a while the screen freezes and I hear three loud beaps (they repeat). This happend three or four times, every time it boots up as if nothing happened.

Than it happend at a boot. The grey start up screen is interspersed with terminal messages repeatedly sagin "8debugger called: ", three loud beeps. Turn off, turn on, everything normal again.

I googled the issue and found out that three beeps signal a RAM issue. However most sources agree on the fact that system diagnostics are only run at startup - so this should not happen in other modes of operation. Also I'm puzzled since it did not always hang with three beeps (I got a “regular“ kernel panic most recently, with that black PNG in the middle of the screen, telling me to reboot).

Also I did a memtest, which reported no errors. It may be worth noting that every time the problem occurred I was playing some flash video. system.log and kernel.log do not contain any error messages (at least none relating to a kernel panic). 

What may be the cause of this problem? Is it possible that the RAM is damaged (without memtest reporting an error?) or simply loose somehow? In some forum I read it may be the logic board. Do you think that may cause the issue? What should I do next to identify the problem or better: solve it?
You might try removing part of your ram and booting up; then trying with the full amount or first one then the other. As for acting up/freezing during operation, I recall having this same behavior with a loose RAM stick once so IMO it would also be worth reseating them.
MEMTEST is not perfect BTW.