CV Joint, Steering or Something is Knocking.

Hi, New guy here. I have been a member of ImpalaSS for some time and often found my answers through their forums but now I have a question about my Venture.
 
Last November I drove my van to OKC and while there I started to experience a knocking from what I think is the front passenger wheel area. When it first happened I figured it was the CV Joint because that is exactly what it sounded like except it didn't make the noise all the time. My cousin and I (both backyard mechanics) gave it the once over and could find nothing screaming out what the noise could be. Drove all the way home and didn't here the knocking at all. Three weeks later it knocks for about 40 miles and stops. Goes silent for 3 months or so and appears again making racket for forty miles or so.
 
It almost seems like something is sticking out from the wheel assembly and hitting the floorboard every revolution of the wheel but when I check there is nothing.
 
I have basically gave up looking for the knock expecting the knocking part to fail by now so it could be replaced but still nothing but the intermittent knock. The van just hit 120K and we plan on using it for vacation this year but I would sure like to get rid of the mysterious knock.
 
Does anyone have any insight into what the problem may be?
 
Thanks

Engine mount
strut or spring
wheel bearing
worn bushing
 

Thanks for the response. I do have some further questions based on it though.
 
Would the wheel bearing be intermittent?
 
Also what bushing? I am drawing a blank.
 
Is there an engine mount down by the right front wheel?

wheel bearing dont knock they squeal and they are not usually intermittnet, they will squeal all the time and just get progressivly worse..
 
CV wont usually knock unless cornering,
 
I have heard of transmission mounts causing a 'knock' even fooled a certified mechanic, here in town on his Trailblazer, he told our tech he was on drugs, actually all it was was a rock stcuk between the rubber and the metal mount, cause him some grief...
 
check the top of your strut towers, may be worn bushing here or loose nut, not to sound like a broken record but it BC rocks play havic on vehicles, from breaks squealing like mad, to strut towers 'kncoking' on and off to tranny mounts....
 
Engine mounts I would think you would feel it twisting a bit under the hood from the rubbers being bad, but if it is not completely broke you may just get a knock,