[JRTJH]

Occasional wobble/rattle while towing? Is there any indication of where it may be coming from? Do you have any "sequence that causes it"? Anything particular about the sound or feel?

Some guesses that may or may not be "even close" to the cause:

1. Is the trailer ball tight and secure?
2. What size coupler pin are you using? Is the receiver or hitch pin hole elongated?
3. Are the weight distribution bar brackets tight on the trailer A-frame?
4. Have you checked/regreased the wheel bearings on the trailer?
5. Are the spring shackles/bolts secure and not worn? OEM shackles have a tendency to wear the holes and elongate them.
6. Is the hitch head secure on the shank with the bolt holding the washers behind the head tight?
7. Are the trailer axle U bolts properly seated on the axle index pin and are they properly torqued?

As I said, the above are only WAG's. With no explanations other than what you posted, most anything would be a guess.