On Fri, 17 Feb 2006 12:44:46 +0000, Kate wrote:

Another prospect is that the bars are acting as open-ended organ
pipes; these would almost certainly resonate at audio frequencies. The
solution is simple: stop the airflow over the openings.

If, as I suspect the rails are acting as organ pipes, I wonder if
sticking something to the outside of some/all the bars would be
sufficient to break up the airflow?

Self adhesive draught excluder perhaps?

sponix