Put the tranny in neutral and let the cluttch out when you're coasting and see if it goes away.
Does your car have the 2 piece drive shaft?
If so, check the center bearing.
96 T/A, Black/Graphite Leather, T-Tops, 6 speed, 10 speaker Delco/Bose "Monsoon"
Original owner, 193k miles and counting.
Total engine rebuild at 187,020 miles. AIR delete, bored .030 over.
Comp cams Xtreme Energy LT1 266HR-14 street cam and springs.
Custom leather interior at 190k miles.
In the paint shop now.