tweeter noise

My MTX tweeters just started making a clicking sound.  They only do it with the engine running and stereo on.  They even do it when I remove them from their dash mounting brackets and hold them in my hand  - so I guess that rules out vibration from the car.   The car is an old Lotus with all new stereo wiring with good grounds.   They are wired right into my head unit with the crossover they came with.  I even tried running one off of the amp, but it still does it.   I recently put in a better ignition system and the clicking started around this time.  I've looked at all of the ignition wiring and can't find anything that would be interfering with the stereo.  Is there anything else I can do?  I don't want to buy new tweeters and have new ones do the same thing.  Is there an inline filter of some sort?  Any suggestions?

Thanks,

Ray

Thanks for your help.  I added a ground strap from the engine to the frame and put on some wire separators to keep the ignition wires away from each other and the engine, and the clicking is gone!  Thanks again.

Ray