Look for a loose tie rod end. The steering probably wanders a little, too, doesn't it? Too much clearance on the sector gear preload in the steering box can cause a wander or a shimmy, but it would really have to be loose to get a knock.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!