Stiffer springs will exaggerate any issues previously had that you may of not noticed.
Assuming everything is tight if you’ve not had a alignment after springs then that’s your first point of call.
However if that doesn’t solve it. Simple things like checking Your tyre pressures is a good place to start. Then, wheel balancing etc
However another culprit could be worn bushes or shocks if your car has already done a lot of miles.