Brakes going THUNK


#1

2002 Cavalier with 130K. A couple of months ago, I had the back brakes replaced. Just in the last couple of weeks, after coming to a stop when I take my foot off the brake, there’s a loud THUNK and sometimes a forward lurch. It’s not as bad when I very gently ease my foot off the brake. What is this? Is this something the brake shop messed up? I need more information b/c if I go in cold, they will try to charge me for additional services.