k..it seems like its a faster knock but it dosent seem to match the tapping sound from the top. and when i rev the motor the top tap stays but seems like bottom goes away..it dosent get loud and dosent seem to keep pace with the rpm's while reving. but the top sound does mtach the reving rpm's .could the top end sound cause the lower sound? the quad ben well taken care always had amsoil 20-50w oil, oil filter changed..but never had valves adjutsed ect.