Stop in for a cup of coffee

krazykuda said
Could it be something worn in the front end??? U-joint???

If it comes in at one speed and goes out at another, then it is harmonic - which is usually a balance issue or loose/worn component...

Try to determine what engine or road speed it kicks in and goes away... Does it happen in all gears at that RPM, or just hi gear???

It's the engine. Not the drive line or the front end. It happens under light throttle, any gear. When you give it gas it runs smooth. It's been running this way since I bought it.