Need a cheap "radiac" for Haloween

I am somewhat of a laymen when it comes to electronics but hope that you can
point me in the right direction. I want to build a "radiac" as part of a
Haloween prop.

Basically, I intend to put a few cheap components inside a small cardboard
box with a handle... paint it yellow and put the familiar magenta radiation
symbology on the box. Then I intend to use an old curly phone cord to
connect to a paper towel tube to simulate the "sensor" for the radiac.

I poked around at my local Radio Shack and came up with a Piezo Buzzer that
blows at about 90db using a 9V battery which is plenty loud... almost too
loud but I figure I can muffle it when I mount it in the box. I think I can
just put a simple push-button in line with the 9V battery and the buzzer for
that part. However, I would prefer to have another sound as well... the
sound of a Geiger counter... click-click-click... needs to be fairly loud so
people can hear it in the din-of-party-noise or as I go door-to-door...
preferably with a thumb wheel to raise/lower the periodicity between the
clicks as I wish.

I am open to working with simple things... capacitors, resistors, speaker,
switches, etc... and a little solder but don't want to spend much money on
this project. Any suggestions?

Thanks in advance!
Chip