Was driving down the highway when my speedo slowly started to decrease in speed until it held at about 35mph even though I was going over 60mph. It started making a grinding noise coming from the dash. But when I slowed down to anything under 20mph, then start to get going again, the speedo works fine until I hit about 45mph then it will start grinding again then drop to about 25mph. anyone know whats causing that? thanks guys.