well a quick google search shows a heap of issues with the Sapphire cards  

but - I'd suggest having a look at that "paged pool memory" section on the link above.

P.S I take no responsibility for what you change  

Paged Pool Memory Issues (Looping Sound Crash)

These crashes are most commonly a result of running out of a special type of memory called paged pool memory. Paged pool memory is allocated by the OS kernel for use in applications such as Direct3D resources. Running out of paged pool memory can result in Direct3D crashes (a.k.a. game crashes) and in the Steam.exe process using 100% of the processor. In some cases you may get an error message stating there is an issue with paged pool memory and/or there will be black textures and missing models. In most cases, you will not see any such error message - your game will simply crash and the sound will loop.

Update:

http://forums.anandtech.com/messageview.aspx?catid=31&threadid=2221236&FTVAR_STKEYWORDFRM=&STARTPAGE=1&FTVAR_FORUMVIEWTMP=Linear

I found this during my googling and have now 'flashed the bios', I think.....

5 and a half minutes of Richard Burns Rally at fullscreen, which is a record, so it may have done the trick.  Thanks all for your input, especially Azza for pointing me down this trail and Kristof for the testing programs.

I'll do a half hour in RBR now, just to make sure of course.

Well, the bad news is that the wife may miss me for a bit over the weekend.  

The good news being that the bios flash seems to have done the trick!  

Again, thanks for all of the suggestions and help guys!  Truly appreciated.   

Nice one, should have known about the Sapphire bios thingy as my colleague had the same issue a few months ago 

For testing the stability of a(n overlocked) gpu you can use furmark