One important thing to remember is we're spoiled to QUITE vehicle cabins these days. So isolated from the normal mechanical noises our vehicles make that they could be electric and often times not be much quieter. AD trucks are not like that. You hear every little tick and tock, clank and possibly knock (hopefully not a knock).
The above said, if the valves are not properly adjusted, a 216 or 235 can be a lot noisier than it should be. So, make sure everything is as it should be and then check out a rpm/speed calculator to determine how many rpm you're turning at a given speed and don't worry about how things sound. If another stock AD truck is in your part of the world it might help to ask a ride just to broaden your experience base.
