Go here and follow these directions:
http://www.neons.org/neontsb/diagnost.htm
If you get a code 11 I would have it checked ASAP. Never fool around with a timing belt issue. If anyone tells you the Neon has a noninterference motor, they are wrong. If your timing belt goes, kiss that motor goodbye. Chances are pretty good that if the car had only 28K miles on it when the HG got replaced, then the timing belt was not replaced. The owner's manual does say to replace at 105,000 (I checked for once
) but I always do mine every 60,000. All my past vehicles manuals have said to do it around 60K. If you have just a noise and don't notice a change in performance I doubt your timing belt is the problem.