Assuming the tweeter is fried, would it be an easy fix?
Assuming this is the issue and you can find an exact replacement then it may cost no more than $50 depending on the speaker.
You may also want to check the woofer though - this kind of sound can also come from a voice coil rubbing in the woofer...
If you have time - swap the tweeters between the speakers and check again to see if the problem moves with the tweeter...