Thanks for your input. I purchased the machine from a seller that buys excess inventory from Home Depot. I have been in contact with Toro providing my bill of sale and the manifest from HD to them showing the mower. It was advertised as new display model. It was certainly brand new when I picked it up. Toro will review my information and decide if they will extend the warranty to me. Fingers are crossed. In the mean time I will check the blades. What ever is wrong has something to do with the left rear of the mower. If I engage the blades and lift the left rear I get all this noise as if something is hitting the underside if the deck. If I lift the right rear there is absolute silence. If I don't engage the blades but use the drive only there is no noise. I looked under the deck for signs of something hitting but saw nothing. Tomorrow I will pull the front cover and check there. I will also check the position of the blades. There is absolutely no vibration and it mows perfectly, except for my stated problem.