well thought i would miss the dealers this time and have a look my self , lifted the engine cover slightly and my mate revved it for me , i could hear and feel the "thud" but could not really see signs of anything wrong.
so i thought i would take the whole cover off , again couldnt see anything wrong , but i did have a new grren panel filter fitted a couple of weeks ago , so took it out and swapped it back for my standard filter and viola , noise gone.
very strange.
will ask JKM about it.