Tweeter Distortion


I have an old pair of Merlin 2B plus speakers which I love. I know- they are ancient, but great!
Anyway, recently, I begun to hear distortion in the tweeters. It's coming through from all sources. I don't remember blasting music, or even listening to loud music. It is most apparent in vocals, and in some string instruments.
They are biwired with Kimber Kable, and my amp and preamp are all working fine.
Is it possible that both tweeters need to be replaced, or could it be something else?
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I'm thinking with starting with purchasing a contact conditioner.
Any suggestions?
i do not use it though many here do. i somehow feel like crackle should not be helped by contact conditioner. crackle strikes me as an electrical/circuitry/capacitor type issue. i could be wrong...does not hurt. just make sure to dry well before reinserting.