My Valves have been tapping ever since I've replaced the timing belt. About 2 yrs ago. My timing belt had a couple of missing teeth. Anyway My truck's valves tap for anywhere from 8 to 15 miles down the road then tey quiet down. I have no power loss. But it does seem to help if I run Midgrade gas. Whats the best way to address this issue short of having the head rebuilt or replaced?