Well certainly the warranty route is the way to go. IF it has expired, you might have better luck by posting the engine make and model numbers as it is likely that others, besides myself, haven't the faintest idea what SR4 20055 is.

Walt Conner

SR4 20055 is not a model I'm familiar with.

The only SR 20055 I'm aware of was a rear wheel drive personal pace mower made by Toro. I believe the model is about 5 years old, so depending on when you bought it the 5 year warranty could be expired or close to expiring.

Is that the mower?

A rat-tat-tat noise could be from several causes including a very noisy valve, bad bearings, blade hitting the mower frame and a leaky exhaust.

Have you hit a rock, stump or other object while mowing? Have you actually checked how close the blade comes to the frame? If not that's the first thing I would check.

Yeah, it's the Toro Super Recycler 20055. I checked my receipt and I got it in May of 2007, so it's still under warranty ... off to the dealer to let him figure it out :-)

Yeah like RB said could be a multitude of issues . A engine or mower normally does not just begin to make unusual noises . Something has happened to cause the issue . Lack of oil , maintenance , misuse ...etc. Bring it to someone knowledgeable with small engines .