My car has been leaking oil for awhile, and I know that it needs to have its rear valve gasket replaced. After it hasn't been started for more than a few hours, it emits a whitish smoke, which I was told is pretty normal when the car has a leak. Recently, however, the car has begun squealing for about 10 seconds, in addition to the smoke, if it hasn't been started for a few hours. Do you have any idea what might be causing this noise? Could it be releasing a vacuum? Is it a serious problem?