It sounds as though it is suffering sticky tappet syndrome, put some wynns engine flush in there, and here it get quiet within a few miles, worth a try has nearly always worked for me.
Make sure it is on the correct 5/W30 oil as these are very sensitive to oil, but I would change it anyway(+ filter) after you have run some engine cleaner through there, you are quite safe to leave in for a few weeks, I do rather than 10 minutes that it says on bottle.
tabetha