MsMpEng.exe and MRT.exe causing excessive HDD activity

[StGeorge991]

The title is mostly self explanatory, but here's some details.
I know what MsMpEng.exe and MRT.exe are. They are, as I've understood, Windows Defender and Microsoft Removal Tool, respectively.
The problem is, whenever PC is idle, for more that couple of minutes, my HDD goes into overdrive, and last couple of times, I opened up resource monitor to see which programs were most active, and it turned out to be these two.
This started on completely fresh installation of Win 8.1 from basically the first day. At first, I thought it was Windows indexing service, but I found out that it wasn't.

My question is, can I disable/remove these culprits and how?

My configuration is:
Intel i3-3240 3.40GHz
8GB DDR3 RAM
MSI AMD Radeon HD 7700 1GB DDR5 VRAM
System HDD HITACHI HDS725050KLA360
Secondary HDD TOSHIBA DT01ACA100

 

[Debaditya Ray]

These two links might help you

http://answers.microsoft.com/en-us/protect/forum/mse-protect_scanning/msmpengexe-excessive-disk-usage-problem/63816ff0-f27a-4cf0-9337-ad5b4bf9124a

http://answers.microsoft.com/en-us/windows/forum/windows_xp-performance/the-program-mrtexe-keeps-using-50-of-my-cpu-all/c761db2d-617b-e011-9b4b-68b599b31bf5