A weird whining noise

A few days ago I started getting a weird whining noise coming either from under the dash by the steering wheel or from under the hood on the driver side of the car. I can't tell for sure because I have no safe way to open the hood and stick my head under it while the car is moving.

I don't get the nose while idling or while driving very slow, like 5 mph, but as soon as I drive faster than that, it starts whining. And the pitch gets a little higher as the speed goes up.

I took the car to Tom, a semi-retired mechanic from some eastern European country who knows Mercedes cars inside & out. He took it for a drive around the block, then he pulled out the gauge panel and put some grease on the speedometer cable. Apparently when it gets too dry it makes that annoying whining sound. I pay him $20 for his time and I'm on my way. Gotta love those easy fixes!