This is the sound of an IBM C Executive with the cover up

https://drive.google.com/file/d/0B8YQXfsZjIsQcy1LLUFYQlpIQUk/view?usp=sharing

The only thing which bothers me about this is the highest pitched portion, sort of a rhythmic fine rattling audible outside the typewriter. The machine did not make the higher pitched sounds until I had gone through about half a new ribbon. Any thoughts on how to track down this noise and eliminate it?

(You may get an Unable to Process Video error but if you download and open the file the sound should play)