welcome to the joys of owning a golf. My car made a similar noise for only one day
I changed the oil right away and have not heard it since...
Here's the link:
http://www.flickr.com/photos/67897318@N06/6797558531/in/photostream/Apologies for it being pitch black and the use of profanity at the end...(thought that was the end of the car...)
There should be a thread: the sounds that mk3 golfs can make...

....bet it would be popular...
It is also a dragon green car...I've been told that this is an unlucky colour by a recovery man and a mechanic......
It may be that you have put too much oil in...as i had done?..(I was putting 4L in a 1.8 where I should've been putting a little less than that..)
Anyway just do an oil change and hope it goes away....worked for me...