Clipping

Tweeters usually fried and silent or audibly distorted as described above.

Other non speaker problems might sound similar. Hook the speakers up to some other source and listen for the problem that way first if possible before drawing final conclusions.

If you have it, Peter Gabriel's "So" contains a great test track that I've used to identify a clipping-damaged tweeter (been there, done that, more than once). Check out Track 8, "We Do What We're Told". No need to listen to all of it...the opening measures before the lyrics will tell you what you need to know. If there is damage to a tweeter, you will hear a scatchy obviously distorted sound. You'll know it when you hear it. If it sounds lyrical and smooth...so far, so good.

Thanks for the info. I downloaded the track from iTunes and it looks like all is well with my speakers, it sounded good.

Great...I should have added, listen with your ear quite close to the tweeter(s) to hear the distortion. When I had a problem the sustained instrumental notes and choir voices in the intro would break up at moderate volumes. But I really needed to be close to hear the "buzzing", as I recall.