Is a Mercury Mountaineer FWD? I thought they came either a RWD or 4WD. But in either case, wheel bearing usually make a roaring sound at highway speeds that gets much worse in a curve. The clunk the OP mentions could be due to universal joints in the driveshaft, CV joints if 4WD, bad trailing arm bushings, ball joints or any number of other things. This will take an “eyes on” by a competent mechanic.