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It is possible that there is some corrosion on the rotors causing this problem. The cold can cause some condensation on the pads, and they often make a spot on the rotor that is worse than the remainder of the rotor, and that is why it pulsates. The corrosion will also explain the grinding noise if the pads are new.
Depending on how new the pads are, there also could be an issue such as a caliper sticking which could wear out one set of pads very quickly. You'll want to be sure to have this inspected if that is possible.
Also, it's quite common to have a little bit of surface corrosion after they sit for a few days in high humidity, but it normally goes away after a few stops. Yours is worse than this if it is pulsating.
You'll need to have some rotors turned at minimum to solve this issue, if the pads are still good, they can be re-used.
Hope this helps solve your problem.
Ok, sorry if I misunderstood.
Sometimes, you can have a rear rotor causing this problem and you might not necessarily feel it in the pedal. If the sound is coming from the rear, then that could explain it.
The other possibility is that you have a tire on the front that is worn unevenly, most likely from being on the rear of the vehicle too long, and then being rotated to the front. If this is the case, you might hear the noise a little bit as you are driving along, but hear it louder under braking because the vehicle transfers more weight onto the front tires.
If there is uneven wear on the tires, you may be able to feel it with your hand. The best way is to look at them while they are spinning on a wheel balancer or with the vehicle on a hoist.
It could also be a wheel bearing. These normally change pitch as you veer side to side when driving. sometimes the noise goes away when turning one direction and gets louder in the other, but not always. These can be identified by running the vehicle while supported on a hoist and feeling the front coil springs. If it's bad enough to hear while driving, it's bad enough to transmit vibration into the spring. They can also be listened to with a stethoscope or by using a long pry bar or breaker bar to listen to it by pressing it against the steering knuckle and your ear.
If it isn't brakes, it's pretty much got to be one of those.