Hi

I'm looking for some advise on a annoying problem with my car

When I accellerate gently, or driving at constant speed, I get this annoying feeling that the car is having a wire attached to the rear, which is being pulled every one second. It is most obvious in 1st 2nd 3rd gear when the revs is arround 2-3000 rpm.
The "rytm" of the pulling feeling, is very constant

When driving at motorway speeds there seems to be no problem, but maybe this is because the problem is masked by the inertia of driving at higher speeds...?
When accelerating harder (2/3rd or flatout) there seems to be no problem at all

car is running MSD closed loop, and coil pack

any suggestion would be highly appriciated

Christian