It could be the hard drives. Do you know if the drives are refurbished by the manafacturer?
Last year one of my hard drives died suddenly (to be honest, I killed it but don't tell anyone!!) and as it was still under warranty, I was able to get it replaced for free. When the replacement arrived, the first thing I did was to run some tests to analyze the structure and bad sectors were found. So, I called the company and arranged another replacement and the same thing happened again. The company insisted it was my PC and I was adamant that it wasn't as all my other drives work without any problems. They wanted to arrange collecting my PC and checking it over but I wasn't having that so I complained until they agreed to send me one more and all has been fine since then. I also managed to blag a free hard drive too as instead of returning one of the faulty drives to the company where I bought my PC, I arranged a sneaky warranty replacement with Maxtor (again, don't tell anyone that bit!!).
So...by all means check your PC out for malware as carsey suggested but keep an open mind that the hard drives you're receiving could be faulty before getting to you.
Have you tried a low level format?