I had the dealer do the 60K service on my 1996 Miata at 59K, including replacement of the timing belt and aux. dive belt. On the day I picked it up, the values were noticeably tapping intermittently (the engine had never made a sound previously). The valve tapping wasn't constant, but would become highly noticeable and then quiet down. Took it back to the dealer and they supposedly adjusted the values and said it was probably just loose carbon causing it. Still have the same problem. Any suggestions?