1 random BSOD per day

I'm running Windows 7 home premium, 64 bits. I get one (and only one) BSOD each day, no discernable pattern. The BCC code is different each time. Last time it was c5, the time before that it was 50. It's been happening for a while now, so I no longer remember if the timing coincides with any Windows updates. I ran memtest86 based on some info I found from googling one of the bcc codes,...