What happens if clients contact me after a non compete agreement?

The answer completely depends on what you do, and if the activity is prevented by a valid noncompetiton agreement. Noncomps are very technical and thus its difficult to know without a thorough review what is and what is not prevented, if what can be done without running into liability moving forward. If you're leaving your old job and considering taking on individual clients in a new capacity, you should contact an attorney to assist you. It really doesn't make much of a difference if it's an old client or not, as noncomps can prevent you from competing with your former employer, regardless if it's a former client of their's or not.