I've had a million things replaced, including the spark plugs. Which I thought solved the problem because it started right up and ran fine for about a week. Now, it doesn't want to start again and whenever I press the gas sometimes, it takes it a minute to go. What could this be? Also, I got new tires last week and now whenever I press the brake, it makes a 'flapping' noise.. kind of like I have a flat tire.