slow rising grating sound

Hi all,
can anyone help me devise a slow rising pitch, which is grating in pitch, using the 555 Timer if thats the right chip to use? of course there would be a variable resistor ...for R1 & R2 but cant work out the valules for C1 in pins 1 &2 of the IC.. would it need a Transistor output needed..?

Im going to just drive a pizeo element..
thanks very much for ANY INFO I cant work it out ..

cheers
vortex2009

I would probably use a NE566, assuming you can still buy it or a VCO made with op-amps or comparators.