500E steering makes loud noise when warming up

[hedpe]

Alright, when I let the 500E sit in the garage overnight (12 hours or so of rest for it), and i get up in the morning to drive it. When I start her up she runs fine. Then I back out of the garage, as I do so and turn my wheel, something makes a loud noise, loud enough to hear both in and out of the car. If I don't turn the wheel it doesn't make the noise. It's a loud buzz/hum noise. It only does it for about 1/4 a mile and then it stops once the car is warmed up. If I park her for 4 hours or so then come back, she still won't do it again. Only when I let her sit for about 8+ hours. It's whenever I turn the wheel left or right it does it, if its going straight, I get nothing. A new steering box was put on recently, but if I'm correct, it was doing this before and after the box was put in. I can't remember if it was doing this when I first got the car or not. Is this something normal or is something wearing out?

[csnow]

My first guess would be that the belt is slipping. Symptoms match well.
This would be easy to observe.
Just have someone turn the wheel back and forth while it is cold, and watch belt for slippage.