Like metal scratch. Do I have to replace a new one?

Let it go until it dies. You'll know it. You won't be able to start the car

When that happens, replace BOTH the alternator and the battery at the same time.

Are you sure its the Alt. Your discription of a metal scratching sound also matches the sound of an AC compressor clutch bearing. Check again and be sure its not coming from the AC compressor.

I just installed a shorter fan belt in my 250,000 mile 92' because I didn't want to replace the AC compressor.

Use a stethascope to narrow the sound, good idea to replace the bettery and the alt together

Yes. I removed the belt and rotate the pulley of ALt. The sound is there.

Why I need replace the battery? It is a year new one .

A failing alternator will stress and kill a battery. This weakens the battery. So when you put a new alternator on a weakened battery, it stresses the alternator. Get it? You get caught in a replacement cycle. Do both.

If it'* coming from the Alternator its probalby the rear alternator bearing.. The new style alternator is more compact than older alternators design and creates more heat ( but amperage too ). If you narrowed it down to the alternator.. just get a can of WD-40 or whatever spray lubricant you have with a straw attatched.. start the car.. and douse the rear bearings with the lubricant.. if that quiets it down.. there'* your culprit.. and if you feel saavy and have enough time.. get the bearings and change it yourself ( might be wise to invest in an alt rebuilt kit since you're going to tear it apart anyways )

I would say you do not need to replace your battery. Your complaint is a noisy bearing, not zero output. Your altinator may continue to work for yrs, mnths,weeks, or hours. Just can't tell. But unless you have an engine light on, your altinator is working. If you have a gauge on your dash, or a multimeter check for 14+ volts across your battery while the engine is running. If you do than great. Altinator is putting out, but your still left with the unknown of when will it die.

I bought a LIfe Time Warranty altinator from Autozone about 4 yrs ago. I just had to replace it again couple days ago. That was when I noticed my AC compressor issue. I got a new $130 altinator from Autozone under warranty even though I couldn't find the reciept. They had me in the computer. What a deal!

I would recommend getting a new Altinator from a parts store that will give you a life time warranty.

Please add your cars trim and year to your sig so we can better help you. Also include your location so we dont say autozone to someone from Canada where there are none?

The Bonneville charging system in general is notorious for revolving alternator then battery replacement cycle. Its good advice to say replace both as that is going to be the out come. Having a life time warranty is good, but does nothing when the nearest company rep is 100 miles away in the middle of the night on a Saturday? Treat the alternator and battery as one and safe motoring I say.