Bad Sound in my engine

[HDEUCE7]

I have had a unsual sound develope in my engine. In the morning, usually when it is a bit chilly, When i start my H2 a large whine developes. When i accelerate the whine gets louder and when i apply the breaks the sound developes a lower pitch and quiets down. It last for a little while, then when the engine warms up it stops. People have told me it probably is the tension pulley but i don't know. And the hummer mechanics haven't been much help because the sound stops before i get to the dealership. Can someone give me a suggestion on what i should do.