I had a PC that would corrupt disk transfers every once in a while... I'd mainly notice it when I'd copy 70gigs of flacs to the system. I'd find a few of them that would not test/extract without error. Memory testing would not find a problem like that.
I suspect a hardware problem though it could be software. Bad drive, bad disk controller, bad disk, memory, etc.
Maybe try copying WAVs and verifying the md5's. But keep in mind if you have a disk problem the clock may be ticking to a complete meltdown.