I get a knocking sound when making left turns or when going over bumps slowly. It doesn't make the noise when turning right or when on the highway.

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The most likely reason is worn CV Joints just behind the front wheels.

It could be several things ....
Wheel bearings - jack the front driver side up. First ... just rotate the wheel ... you should hear NOTHING. Any noise menas there is probably a wheel bearing/hub issue. Now take hold of the tire in the 9am and 3pm positions. Try to push/pull from side to side ... if there is any "play" in the wheel the bearings are going.
Brake line interference - a lot of brake lines have a plastic sheath in the wheel well area ... check to see that the line/plastic sheath shows no wear when you have the wheel off...that might cause the issue.
Steering linkage - even though the upper control arms were recently replaced look at all the ball joints and grab hold of them and see if there is any play/movement.
Repeat on the passenger side..
Good luck on your troubleshooting

I would say it sounds like cv joints need replacing.also check bushes and ball joints for play. If ok turn steering on full lock both ways.start with full lock on right turn pull away slowly if you get knocking noise you will know it's that side is worn and then do same on left turn on full lock.

Ensure the wheel nuts and Axle nuts are properly torqued to the specification. Lift up the front wheels, place supports under the car and do the following:
- Sit if front of right wheel, slightly move it right and left and feel any abnormal noise if coming out of it. If click-click or Tuck-Tuck sound is observed it could be due to the excessive play in the tie rod end, rack end, ball joint wheel bearing or U joint. Next hold the Tire with your one hand at the top and with other hand at the bottom. Shake the Tire inside out and feel any noise or play. If play is observed, it could be the worn out ball joint or the wheel bearing. Now hit the Tire at the top with rubber hammer and observe any rattling noise coming from near the center of the wheel. If you could listen to the extra noise it could be due to the dried up caliper pins. Grease the pins with graphite grease. If all is found fine, similarly check the left wheel and repair as necessary.

It could be a hub bearing, or CV joint in the axle, or a faulty tire.
You could move the tire to a different position and see if the noise moves with it.
Usually a hub bearing will make a roaring sound not a bump or knock, the CV joint can clunk as the axle turns.

Suspect worn outer cv joint. Check the boot for any tears, damage or leaking grease. If these are present your cv joint will fail soon if it hasn't already. If you put the car into reverse and turn the wheels to a hard lock a bad cv joint will make a popping grinding type sound. Try left and right turns when doing this test.

There are a few suspension parts that can cause knocking noises. Such as swar bar loose, strut mounts going bad. You should really have a shop do a complete suspension check.

The knocking noise on your van is front sway bar bushings

Sounds like your left front wheel bearing is going bad. When you make a right turn, or compress the right front suspension over a bump, it forces the car to roll to the left. This loads the suspension on the left side, which will exaggerate a wheel bearing problem. Are you hearing the noise at all when travelling on the highway in a straight line? If so, it'd be either a grinding sound or a hollow humming noise. If you aren't, it may be that the bearing is just starting to go bad.

A quick test to see if the bearing is bad is to jack the car up at that corner, grab the wheel at the top and bottom, and shake it hard - if there is any movement or looseness, your bearing is shot. If there is none, it doesn't mean the bearing is fine, but it could be that it's just starting to go bad (which would be why you only hear it in turns and bumps, but not straight-line yet).