OK, took some time to get situation updates because im currently serving in the (Finnish) army right now and I don't have much free time. Nevertheless Stu and other were right, the belt was too tight. It got loosened and the noise decreased drastically. I did little test drive after and came back just to hear the noise was back.. I opened the bonnet and tested the cambelt, and it seems to be too tight again. So somehow the belt tightens itself. But after all the culprit and solution is found and as I have time I will order new cambelt kit and camshaft bearings just to be safe as Stu said.

By the way should the camshaft bearing change be easy job or is there anything important I need to take into account?