TLinMN

2003 tls with 314,000 miles. There is a vibration at very low speed -less than 5mph...not a brake pulsation of any sort. It's not really even a vibration. It is more of a sound -very rapid brrrrrr sounds. I can feel it in the brake pedal as I lightly touch or firmly apply the brakes at this low speed. The odd thing is that it will make the sound that I feel in the brake pedal even if my foot is not on the brakes. It's almost like it is a brake sensor or speed sensor type of thing. Does anyone have a suggestion or solution?