Safe Mode screen flickers

Is it normal for an iMac, when in Safe Mode, to flicker when scrolling through Mail?

I don't know if this is related, but I'm trying to run the computer in Safe Mode for a while because, out of Safe Mode, the computer will randomely shut down...suddenly...just like if you pulled the power cord out! Also the hard drive runs ALL the time, it seems (though it's quiet right now, in Safe Mode).

But again, the question is, is it normal for the Mail program to flicker as a result of putting the computer in Safe Mode?

Thanks!