I'm hoping someone can shed some light on what may be the cause of my Toro mower problem. It's a model 20332 22 inch recycler with the Ready Start start system. I bought it in 2009. It isn't my favorite mower with all the problems I have had to fix. This one has me stumped. It starts up on the first pull every time but during the first two minutes until it is warmed up it randomly makes a very muffled popping sound. It's a muffled pop - not like a backfire. After it's warmed up in about 2 minutes the idle is very even, no pops and it sounds great. Anyone have any knowledge or experience with this type of problem ? I've done a ton of work on this thing to try to fix this problem; new intake gasket, cleaned carb, new carb to intake o ring, cleaned combustion chamber, new air filter, aligned Ready Start air vane to thermostat and nothing has somewhat improved it except a new float bowl gasket - but it still has the occasional pops when cold. Any ideas? Thanks