Clocking,notchy noise when changing

I have recently noticed a slight clocking, notchy noise when changing gear, especially when going into 3rd. It only happens now and then. The car only has 45k and it didnt happen when i 1st brought it. What could it be?? any thing to worry about. Might show the local specialist, when i get a chance. Thanks any views??

Does it happen when you push down the clucht and then when you release the clucht, can you only hear when the windows are open. If does then it will probaly be a rattling drive shaft that needs rebonding. Had it on mine and drove me mad.

Ohk...any other things it could be... If so how much are we looking at.? Thanks