So I was taking the trash out tonight which entails using the 2305 to haul the cans down to the end of the driveway and I noticed a persistent rough ride/bumping feeling as if there were flat spots in the rear tires or I was driving over small speed bumps every 20' or so. The driveway is a quarter mile long and paved and the machine did all the way down and back. I checked the machine over and otherwise ran fine. Impossible to have flat spots since it sits for no more than five days a a time. Any thoughts?