Laptop freezes for 2 - 3 seconds every so often

Gents, I would really appreciate your help. I have read hundreds of fora to see if I could find a similar problem, but no solution that worked for me.

Here I have a laptop Dell XT2, Windows 7 OEM installed, Office 2013, Chrome, Bitdefender on it plus some minor software. The laptop is one of those 'tablet' style things with a stylus and so. I really like it.

However, lately the laptop freezes for about two or three seconds, then continues as normal. It seems to do that right after I clicked something or hit a key. The disk activity LED goes on, presumably the disk goes to 100% (although I cannot be sure, because performance monitor also freezes). It does remember any keypresses and also mouse movement is captures, because after the freeze, the character I typed are spawned and any mouse movement seems to be correctly captured.

I have run malware detectors/cleaners, anti-virus, etc. Nothing. At first the tablet did NOT show these characteristics when I ran it in SAFE MODE, but now that makes no longer a difference. All drivers are installed correctly as far as I can see. I have run all updates from the official DELL site. I have updated the BIOS. No difference.

TWICE I have wiped the disk clean and started from the OEM installation partition (and updated all drivers again), however, it does not make a difference.

I have run the extensive built-in DELL hardware check. Everything is reported OK.

I have checked the disk with S.M.A.R.T. software, everyting is reported OK.

I have no more ideas what to try. Any ideas would be great!