[folivier]

OK, here's my duhhh moment. On our recent trip out west Cindy's speaker (the one for the stereo) started buzzing. Oh well I'll just replace both when we can find a set. Turned out it was the latch on the overhead panel that was buzzing as we cruised down the highway! Luckily she figured it out before I replaced a perfectly good set of speakers. It tightened the screws and it's been fine since.