Audio Systems: distorting 6x9, crackling noises, input level

Question
Hi I have just installed a new set of 6x9's into the rear of my car and am running them of an amp. They are 350W max pioneer's. When I play them at low sound levels the tweeters on them play a lot of static and crackling noises but then when I turn them up to a fairly high volume the static stops. Whats happening and how can I fix it?

Answer
Hi Carl,
I cannot put my finger on it from here but have you checked the input level on the amp? Needs to be about 75% for normal running. Also have you set the levels on the head unit? The speakers only usually reflect what is put into them so start at the head unit, leads, amp, speaker leads. I doubt it is anything to do with the speakers.
Peter