Hi, I have a 22inch self propelled walking mower , Craftsman . This is my 10th summer using it. I noticed the last few weeks that when I first start it , the mower is very noisy, almost doesn't sound good, but after 15 minutes it runs fine, for a mower this age. What can I do to improve it's condition so it will last a few more years ? I change the air filter, the oil and I spray this carb cleaner in the carbeurator every spring before the first cut of the season. I live in upstate NY and I mow once a week, takes me a little less then an hour. Thanks for everyone's help in advance.