Thru a call to Simplicity they confirmed that the noise usually stems from a low fluid level. In 1996 you must remove the seat and fuel tank, Unscrew the breather and and measure 1 1/4 from top for fluid level. I decided to change and per there recommendation I put in a Premium grade 20/50 after sucking the old fluid out. It appeared I was about a quart low, explains noise. Now I can drag race my 1600's on the lawn. The old one is faster because it has 10 inch tires instead of the 8 inch in 1999.