LV2TNDM

Those are most certainly not DT 340 or 540 hubs. These DT hub models utilize a star ratcheting mechanism in the freehub body. The hub shown uses pawls, so it is not these DT models. Plus, the hub shell shape is wrong for DT, unless they have some lower-spec models that I'm unaware of (which may indeed be the case).

Regardless of the hub brand, you will need a generic bearing puller tool set and press to service the hub fully. This hub appears to use radial sealed cartridge bearings. They handle radial loads very well. But side loads can cause issues, as can overtightening the bearing adjustment. In general, cartridge bearings should have some side-to-side play (felt at the tire), whereas cup and cone bearings, and radial contact bearings (used in Chris King) should not. There are exceptions to this rule. Mavic wheels usually had side play, whereas White Industries hubs do not. Depends on the brand and the way the hub is assembled. You probably need to pull and replace all the cartridge bearings in the hub. Pulling the seals, flushing and regreasing very well may not resolve the problem. Once a cartridge bearing goes bad, overhauling will not restore it. Enduro Bearings in Oakland supplies bearings for many manufacturers, distributers and retailers in the bike industry. Find an LBS who can order them. If you don't want to perform the repair, then find a shop that can.

BTW, you never specified what the problem with the hub was. What symptoms are the hubs/wheels exhibiting that indicate they have a problem? It's very important to describe the symptoms instead of trying to diagnose the problem. Only with symptoms can someone with the proper knowledge diagnose the problem and suggest possible solutions.

Edit: sorry, I missed your reply that described the problem a little bit. A grinding sound or vibration feeling is probably bearing-related. But it could also not have anything to do with the rear wheel. When does it happen? Coasting? Only while pedaling? Only while pedaling hard? Could be the quick release. Could be the wheel not secure in the dropouts. Or if the frame has a replaceable derialleur hanger, it could be that. Or the rotor or caliper rubbing? Chainring bolts? Bottom bracket(s) and/or eccentric? I've seen someone go over an entire bike's drivetrain chasing a creak only to find out it was the pedal!

I'll add that I've serviced several hubs like this over the years that develop roughness in the bearings. Dirt and other contamination cause the bearings to become rough and the axle to creak under pedaling loads. You might resolve the issue simply by servicing the freehub body, pawls and axle, spacer(s) and locknut(s) without having to pull the bearings. Sometimes fresh grease eliminates creaks and groans created by the high forces produced by a tandem.

Good luck.