John Mellencamp's last album was more or less straight-ahead rock, but there's something dark and unshaven about his new one, Human Wheels. Oddball instruments pennywhistles, mandolins pop up like disordered wraiths over gritty drum tracks that sound like they were recorded in a cluttered cellar. Mellencamp himself mutters and snarls in a voice of tangled complexity, worrying his way through songs about trouble. What's on his mind, especially in the hair-raising opening track, ''When Jesus Left Birmingham,'' is the queasy balance between hope and despair. ''When those crazy nights come callin','' he almost screams, we're all left alone, threading our own paths toward an uncertain salvation.
This, in other words, is a pretty heavy record. But three things (apart from the considerable strength of every song) help lighten it. Touches of wistfulness unexpectedly appear in Mellencamp's voice, backup singer Pat Peterson shoots electric jolts of black music into the mix, and those oddball instruments are a constant, happy surprise. Mellencamp's band must have had lots of fun. The world may be in a sorry state, but by working together with such obvious joy, these musicians demonstrate how things ought to be. A