Don't rely on HD Tune it's basically rubbish. Test it with the drive maker's own diagnostic software which is free, it's called Data LifeGuard Diagnostic for Windows. Unfortunately, the link to WD's downloads is currently broken, but when they've fixed it this is the link:
http://support.wdc.com/product/download.asp?wdc_lang=en
The same software is also available from a working link here if you don't mind not getting it direct from the developer:
http://download.cnet.com/Data-Lifeguard-Diagnostic-for-Windows/3000-2086_4-10972008.html