[Pills74]

Hi all, wonder if anyone can help. I have read a few post about this before but just wanted to see if anyone had any ideas. I have had my 2004 xc70 d5 with 110000 miles for about 6 months and spent a fortune restoring it as it needed a few things doing. But lately after changing my oil to a thinner grade it sounds like my tappets are rattling and making the engine sound rough. When I start from cold I also get a low thudding noise for about 1 min then it just disappears? I changed my oil back to a 10w40 which helped for about a week and the vac pump which improved the engine loads but I'm now thinking it's tappets. Anyone got an idea of price to have them done, cambelts due next year so will get that done at the same time.
Thanks