I have a 1989 7.4 L OMC with a king cobra drive. When I throttled up this weekend my tach shot up to 6000 rpm for a second and then bounced around for a bit (no audible change in engine). Soon after I could hear a very faint "tap" every few seconds. After doing a quick check I decided it was nothing major (get checked out after the weekend) After a 45 Min run I could hear a much louder grinding type noise (could only notice after slowing down). It does not make the noise in reverse. Any ideas what I should get checked first? It is hard to tell exactly where the noise is coming from. 