ur wd is green or blue?

What's your D drive hard disk? Is it the same hard disk but different volume/partition?
If you're using Green (Eco, 5,400rpm) then you should expect something like this, if your system has not access the hard disk for more than 10 minutes, the hard disk will spin down to slower speed or totally stop (just like sleep mode) to save power, you can however use hard disk management tool from each manufacturer, seagate and western digital has them for their own hard disk, you can set not to spin down when idle, this will speed up your access time but the hard disk will spin more, consume more power and "probably" lesser life span.
My WDC Green 1TB has 1 permanent bad sector (Reallocated Sector Count) and 5 read error sectors (Pending Sector Count), I would backup the whole drive and do some low level format before sending to RMA as the web state that most of the time those RMA return the very same thing back to you, and those hard disk still within acceptable bad sectors margin will NOT be accepted as well.
Hard disk can live pretty long if you give them much care and of course, that's all pretty darn depends on luck as well (it's made by human after all).

Try check your SMART and look for "Reallocated Sector Count", if the amount is huge, somewhere 10+ then you should send for RMA.
Also use the WDC tools to verify the condition of the hard disk, they usually only accept the report from their program, not sure if they will care about how much bad sectors on the hard disk.
If "Pending Sectors Count" is huge, you should experiencing file corruption, then you should low-level format it, normally it should fix it but sometimes later it might come back again (in my case it came back with fewer counts, improvement??)
If every SMART is good then you can run speed test using HD Tune (free or pro can too) to perform speed test to verify if there is speed drop, then try to test few more times before send to shop for RMA. Print screen, print it out and convince them it's the hard disk fault.