There is a belt noise when car starts then it goes away after few minutes. Why is that?

sounds like a loose accessory belt

could be you a/c compressor, you may need to have the pressure checked

if it was mine, I would buy some "fan belt dressing spray" and spray my fan belts or have them adjusted. first spray them once, if sound stops a few days, have the tension adjusted. if spray does not work the first time, this is not the problem.

are you sure its not your fan belts? because if fan belts are not turning, it means that the engine is off. check if the tension in your fan belts are still ok. if not, have it re tensioned. if noise is still present, have it changed.

The squeal is coming from the alternator belt, When the temp is low, the belt is hard and glazed and lost its ability to create friction.

Misalignment of the belt, incorrect belt, worn or loose tensioner, Too tight of an adjustment (many service centers do this on purpose so when the belt breaks in it becomes properly adjusted, I do not believe in this philosophy), The belt is actually one long belt called a serpentine belt.....

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

your whining noise might be comming from dry belts in order to pinpoint your problem have a jug of water ready before startup open the bonnet then startup if the noise appears pour water over the belts if noise goes away replace v belts

Have your power steering belt checked and adjusted, or replaced if worn.

check pawer steering pump belt mybe it is worn out or loose, also check the alteranator belt.