1985 Dodge Ramcharger Vibration and High pitch noise

I just bought a 1985 Dodge Ramcharger. I've been able to trouble all previous problems and fix them myself untill now. Here's the problem, when I am driving and my speed reaches 40 mph my speedometer cable goes crazy and a high pitch sound and vibration comes from the dash. I thought at first it could be the u-joints. So I replaced them. I'm still having the problem. My transmission shows no sighn of needing repair. The truck doesn't shake or wobble and the motor mounts look to be in good shape. I've asked around but nobody seems to have an answer. I'm hopping that maybe someone will be able to help with my problem. Thank you.