I thought that I had posted a suggestion earlier this afternoon, but I appear not to have, as it isn't here! Perhaps it was a dream?
I have used thin plastic sheeting from more tan one source, although they could be described as some form of plastic bag.
The requirements are that it is Thin, Flexible, but not too stretchy and Waterproof. One was a liner for a waste bin, which was thin and "crinkled" when handled. Another was from some form of "Sandwich Bag", but not the standard clear polythene, which stretches and does not vibrate in the same way as the plastics I have used.

By the way, watch out for Mrs.Duck's kazoo tuner. I seem to recall that the first prototype involved plugging the kazoo into a 240 volt mains electric socket!
Quack!
GtD.