Hello, I purchased a 2003 Hyundai XG350 last month. When I start the car, put AC or defrost on, and then start driving there is a screeching noise that lasts for 10 seconds and then goes away. If I stop the car and then restart within roughly 30 minutes, I do not hear the screeching noise. If I leave the car off for about 30-45 minutes, the noise returns the next time I start the car and start driving. The dealer has replaced the serpentine belt, but still the screeching noise is there. Thank you

See if it goes away when you turn the A/C off. The a/c comes on when you sre in the defrost so yo don't hit the windshield with hot air. The screaching is more than likely the A/C clutch trying to engage, that why it was overlooked or ignored by the mechanic. It is a common thing. The battery should be allowed to recoup from the starting of the car which a few minutes of running woll help so the a/c clutch gets full battery voltage to function.. Turning on the defrost and /or the A/c after about 3 minutes of warm up. Open your hood and have someone turn the a/c on and off, you can hear and sctually see the a/c clutch doing its irritating thing.But keep your fingers out off the engine and don't lean over it with loose clothing. Good Luck, Ned