If the problems are odd? Not occurring all the time and different problems occur?
if yes... you might try spin rite . Since the hard drive started getting over 400gb they are never formatted...(yes it would take days to complete)
You may have a simple drive alignment problem, lower cost drives are likely to have a higher rate of problems with this.
Spinrite will rewrite the data so that bad sectors will be identified to the drive itself and moved.
And it can take many hours for one drive...
Steve Gibson - has very good information on his site. He sells spinrite, but all of his other tools are free!
It is worth taking a look. GRC.com