It sounds like at least some of the activity may be illegal, unless the vehicles are properly licensed and equipped to be on a public road. Also, there are noise limits in most cities, which may not apply if you live outside an incorporated town or city.
What you really need is a civil injunction to abate a nuisance. You start with a temporary restraining order that is effective immediately, then seek a longer term preliminary injunction. You will need to persuade whatever judge hears TRO applications in your jurisdiction that the activity is beyond the bounds of what must be endured and that it serves no legitimate purpose. The defendants would be the owner of the land, and any individuals you can identify by name. Are any other neighbors similarly upset, and are they willing to join you in acting against the landowner? You may be able to handle this by yourself (in propria persona) but the assistance of an attorney would be helpful. There are procedural rules that must be complied with, which an attorney will be familiar with. I would start by going to the web site for your county's court system and searching for temporary restraining orders. The site may have self-help info for people in your position.
Especially if these are off-road-only vehicles it may be illegal to operate them other than in a designated OHV park, as is the case in my state. The more instances of "illegality" you can muster, the better the chances of getting a TRO and then a preliminary and ultimately a permanent injunction against this activity. Even if not a total ban, you should be able to get limits placed on time-manner-duration of the activity. Once you have an injunction, it is a court order enforced by the sheriff in your county. Be persistent with the local police and let them know you are not going away.
Unfortunately there is little chance of recovering whatever legal fees you may incur hiring an attorney if you go that route. Good luck, it sounds like the facts and (probably) the law are on your side.
Just for the record I am retired and no longer in practice, so this is not legal advice.