Loud Speedometer!

[kooljunkguy]

The other day I was driving my Phaeton and all the sudden the speedometer began making a horribly loud noise. The dial would fluctuate and it would get extremely loud once I got to about 10-15mph. The cable never snapped its would just get loud, I could reach under the gas tank and push the metal cable housing up toward the speedometer while it was making the noise and it would stop until I let go.
Any idea what I might check first before I begin chasing around for the problem?