Sounds like there may be excess sibilance somewhere in the recording and/or playback chain. This would include the singer.

A high frequency peak or unstability somewhre in the aforementioned recording and/or playback chain could cause this.

The cause can be any of the things you listed. Once a mistake is made in a recording, it is pretty difficult to correct it without the correction causeing problems elsewhere. If the problem is in the playback side, then replacement of the offending piece of equipment may fix the problem.

Or it could actually be Paul Simon actually singing "you broke my fart" etc. Sort of like playing your Beatles albums (remember vinyl?) backwards to hear the message that "Paul is dead" but without the trouble of spinning the platter backwards.

Try playing the recording on a system that has less pronounced highs (or even subdued highs) or used tone controlls to investigate.

Paul

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the 1derful1