Update on this for those who also think their engine maybe a bit on the "diesel sounding side".
My car is currently at Heritage VW in Bristol, they are keeping it for three days to investigate the excessive engine noise, this is after I took it in a couple of weeks ago for them to have a quick review of the noise based on findings of a VW garage up in Liverpool who said it needed a valve replaced (which actually turned out to be a red herring). Apparently they had another one in at the same time for the same sort of thing, but my noise was of a slightly deeper timbre...
Apparently over the three days they are planning to strip the engine and isolate the cause of the sound... then I will need to take it back in to get sorted... joy of joys! Still at the moment it is driving me mad and ruining my enjoyment of the car so I will be happier when sorted.
At the moment I have a great (not) Polo 1.2E as a courtesy car... goes like... stink *ahem*
So, if you think your GTi is noisier than it should be, make sure you take it in...
I am actually taking mine to a dealers this Thursday to have it looked at after I compared the noise of my engine to ROB-MRK5's... mine was a bit noisier on idle... starting to sound like my vRS PD 130 diesel engine 
Mind you, the noise disappears when you floor it! 