L3430 knocking sound while driving (not engine)

[Komrade]

Only happens when driving at higher speeds. Let's say 10mph+
Does not happen if I lift all four wheels and spin them. (Tractor has a backhoe)
Don't believe it matters if 4x4 is engaged
I tried to time it with full wheel spin by putting a marker on wheel and believe it happens more frequently than when either front or rear wheel make full circle.
Driving feels a little jerky uphill, but no knock. Not sure if related, but maybe an axel tooth?
Can I troubleshoot this further without a mechanic?

 

[Jstpssng]

That's what mine sounded like when a tire chain cross link broke loose and was bouncing off the step. Can you have somebody else drive it while you watch?

 

[Shawn T. W.]

Check your wheel lug nuts ... ?