A loud whomp whomp whomp? Does it get faster with speed? Are you sure you dont have a separated tire? I got a crappy set of tires on my tow rig and they all separated at some point and made a similar noise. It also destroyed u joints, shocks and even broke exhaust hangers...
91 Laredo, 4.0ho, TF999, Magnaflow exhaust, Yukon rear axles, Spartan Lockers, Posi locker, 3.5 inch springs, 1"MML, 1"BL, 1"shackles, trimmed fenders, raised flares, 35x13.50s.