Mechanic Q: Knocking noise from steering column?

Sometimes driving over bumps I will hear a knock that seems to be associated with the steering column/ system. I don't actually feel it, only hear it. I have looked for loose items under the hood etc but haven't found anything that may be causing it. It has done this from new and doesn't affect the steering or handling. Even though the knock doesn't appear to affect anything, it is concerning. My son has a 2003 Silverado Z 71 that does not have this issue.