When I release the brake pedal I feel a very faint***** or thug sound its not hard but very noticeable

Driving is smooth, however, when you come to a full stop and apply the brakes; As soon as you lift your foot off the brake pedal, as a driver I feel a faint thug sound almost like a small*****. I had my husband drive to see if he noticed it too, and I sat in the passenger side and we both felt it.