Brake pedal vibration only at certain RPMs

I have a 2019 Mazda3 Premium Hatchback bought new last year. Car is only at 7,800 miles now, but this issue has been there since day one. I’ve noticed that when I step on the brakes there is a small vibration (more like a buzz) in the brake pedal. Now, this isn’t like your normal warped rotor vibration, the car doesn’t vibrate at all, just the brake pedal. And the weird part is i’ve isolated it to only happening over 2000 rpm. I have a manual so I notice the rpms more.

I’ve noticed the road speed doesn’t matter – only the engine speed. Over 2000 rpms I have vibration in the brake pedal and as the rpm’s fall under 2000 rpm everything is smooth and the vibration goes away. Seems like it is connected to engine speed. The higher the rpms the more the vibration. The accelerator and clutch pedals have no vibration. "Vibration" may be too harsh of a word, it feels like you’re stepping on a vibrating smartphone.

Took the car in to the dealer and they said the front rotors were warped and replaced the rotors. They didn’t replace the brake pads since they said they were still good. I took the car home and noticed the vibration is still there.

Wondering what else it could be.

Thanks.