2001 Honda Civic: Strange Vibration at 1500 rpm

2001 Honda Civic, Automatic transmissions, 130K miles: when I’m cruising along at 1500 rpm, usually around 35-40 mph, a strange vibration occurs that sounds like driving over rumble strips and seems to be coming from around the middle of the front axle. Help! My mechanic has looked at it three times, is baffled and I’m running out of patience.

Have s/him examine the inner cv joints on each drive axle. It’s usually the outer cv joints that go bad.