I have a ticking noise, that sounds like a pice of rubber hitting aluimiun. I replaced the timing belt a yr ago when I replaced the water pump.
Have you checked the drive belts? Also the first gen miata's are known to have a lifter tick if they are low on oil. Here is a link that might help: http://www.miata.net/garage/noises.html
Search Mazda MX-5 Miata Questions
Mazda MX-5 Miata Experts