1993 Honda Civic what's shaking

Vibration similar to wheel unbalance, happens at different speeds usually above 40mph, thought it was a balance problem at first but pretty sure its not, its on and off and doesen't always happen. Sometimes its smooth as silk at certain speeds and next time its got the shakes. An unbalanced tire would shake at same speeds every time. This shake happens at 40, 45, 50, 55, 60, 65 then no shake at all for miles, stop for light and its on again. Could it be cv drive axels or a more serious problem? Just got this gas saver and want to start saving, please help!