Thumping in universal joint?

1992 Labaron has a thumping in the front end when driving. I can feel it in the steering wheel and I can hear the thumping when I turn a little to the left only.
The more I turn it to the left the louder it gets and I feel it stronger.
When I turn to the right from center the thumping quits.
I thinks it's comming from the universal joint, but I can't tell.

Any Ideas?