Finally time to put this to bed, although I have a complaint email to send later.
Woke up this morning to a text saying my car was ready for collection, they could have warned me yesterday, but I shot up there before work and swapped back into my car, only ended up getting to work 5 minutes late so no drama.
The final diagnosis was that there was a slight coolant leak and my coolant level was low. So they replaced the hose and replaced the coolant and say the noise has gone. Not had a chance to test it properly but does seem to be fixed! Fingers crossed.
Bit peeved with the way the whole thing was handled though. Its been exactly a month since I dropped the car off and communication has been lacking at times, plus I picked the car up and it was filthy, obviously had been left outside in the rain for a while - just not the service I would expect.
Damn glad to have my car back though.!