Things go more than just bump in the night on Suzanne Vega's utterly beguiling fourth album, 99.9 F°. New York's artiest folksinger sounds as if she'd stumbled upon a deranged calliope band playing in a scrapyard and joined in. Keyboards sound like blasts from a steam pipe; the clanking percussion replicates the sound of someone kicking around an empty bottle. If there isn't yet such a rubric as ''industrial folk,'' then Vega and her new producer, Mitchell Froom, have just invented it.
In other words, 99.9 F° doesn't sound like anything Vega has done before and it couldn't have come at a better time. Her eponymous 1985 debut album still stands as a brittle, evocative mix of singer-songwriter sensitivity and urban imagery, as does her 1987 hit, ''Luka.'' But weak songs and watercolor production marred Vega's last album, Days of Open Hand; suddenly she seemed in danger of losing her cutting edge.
Thankfully, 99.9 F° restores tension to her music. The songs her most consistent batch since her debut are obsessively neurotic and restless. In them, parents and doctors give bad advice or can't help at all; on the churchly ''In Liverpool,'' Vega wanders about the town seemingly in a daze while vaguely pondering a soured affair. She still has her folkish side, heard on the delicate ''Blood Sings,'' about coming face-to-face with a long-lost relative. But the album also has moments of low-key humor (''(If You Were) In My Movie'') and, in ''As Girls Go,'' a deft put-down nearly on a par with Bob Dylan's ''Positively 4th Street.''
What holds the album together are its clangorous, eccentric arrangements, which seem to take their cue from DNA's dance remix of Vega's ''Tom's Diner.'' They're the perfect counterpart to Vega's cool, cautious delivery. ''Blood Makes Noise,'' for example, combines her voice with a grinding synthesizer to perfectly emphasize lines like ''The din in my head/It's too much and it's no good.'' If the sound of thoughts rattling around in one's head could be captured on tape, that clatter would be 99.9 F°. Sometimes it gets a little noisy and very stimulating up there. A