Strange clunk sound/feeling when releasing brake

I have a 95 cavalier z24. When I take my foot off the break it feels as if it is catching and then releasing, causing a clunk sound. Sometimes it is so bad that it feels as if I am getting gently rear ended. It doesnt happen every time I take my foot off the break, and sometimes doesnt happen for days at a time.
I also just got my transmission checked, new transmission fluid and a hose replaced. A month previous I had a full tune up done on my car and I had some spark plugs and my fuel filter replaced. And still I have this nagging problem.
If you could help me solve this mystery that would be great.