I think the responses are varying by climate and I think your rotors are doomed
The pulsing and grinding are the most noticeable symptoms but if you can get a look at the inboard side of each rotor you may see that side rusting up more completely. That "invisible" side of the rotor rusts faster because the spash shield doesn't allow the air to circulate as much.
I have seen rusting that reduced the shiny surface to about 1/2" radially on the inboard side of the rotor.
The only solution is to drive the vehicle more or store it in a dry garage.