Several things could cause that:
Worn shocks/struts
Worn front end parts
Tires out of balance
Drive shaft out of balance
Loose wheel
When you will be sustaining a speed of over 45 mph
The top speed of a Chevy Corvette ZR1 is 205 mph, or 330 km/hr.
I have had the same thing on my 1990 Comanche Eliminator, I replaced the steering dampener, and it went away. my symptom was more like the front end was about to fall out.
Tires are out of balance ( maybe ) A bad u-joint in the driveshaft will cause it too. Check these things.
Warped rotors
allignment
36 mph
your tires may need to be balanced
Normally this is a tire out of balance. Have your tires rotated and balanced.
Tires/wheels out of balance?
Tire out of balance or bent wheel.
check and replace tires and tie rod ends as neccassary