Greetings from Mikey at Just Answer!
Please tell us the year, make, model and engine size of your car.
Please tell us when you hear the noise is it just when the eninge is first started while stationary or does the car have to be moving before you hear the noise?
It is a 2004 Hyundai Santa Fe 4 cyl. I hear the noise when the engine is first starting if the temp was cold or damp the night before, when driving if it is raining, or if the car has been sitting outside for several hours and the temp has dropped. Please note this does not happen everyday.
Hello again. What you are describing sounds to me like a slipping alternator belt. The load on the alternator is particularly high when the car is first started because its charging the battery. The belt is made of a rubber compound and the alternator pulley is steel and it makes a very high pitched squeal when the belt is slipping. As the the battery becomes charged the load on the alternator becomes less and the belt heats up from slipping and gains traction so the noise goes away.
The recommended action is to have the mechanic inspect the alternator belt and replace if needed or tighten the belt if replacement is not needed.
On an unrelated topic, we have been doing alot of engine work on this year Hyundai resulting from busted timing belts. If your timing belt has not been changed on this car yet, its time to think about that too.
Thank you very much!