VCO - parasite AM, thumps and 'theremin' effect

[Smilen Dimitrov]

Hello list!
We just finished our fist ckt ever - it was a VCO, rather simple example of
it really - consist of an OA integrator, OA comparator (comparer???) and a
BJT, which, depending on the sqr output of the comparator, may be a closed
or open switch, which in turn creates the different directions of the
'integrating' current and thus produces the tri output - I'm sure you've
seen plenty of these (I could upload an EWB file if necesarry, or any other
format). Finally, it's working, and it sounds damn nice, but we've noticed
some things:
1) There is a parasite amplitude modulation there too. Any thoughts on how
to evade it - I guess it does add some punch to the sound, but I guess the
output should better stay clean of it.. So we need ideas on how to steer
clear of it.
2) The ckt wasn't boxed or anything and we noticed a strange thing. First
of, instead of resistors used to shape the tri, we used some pots - hoping
to get PWM sqr and saw out of the regular sqr and tri, and although it does
work, something interesting happens - I guess that in such a position, the
cirkuit is on the edge of oscilating - and sometimes you can hear a large
thumping sound - as if you're messing with the power supply wires or as if
a cap was discharging???? Any ideas why this happens and how to make it
dissapear?
3) In the same position of those pots, it acts like a theremin too - I
stand up - the pitch rises - I sit down the pitch falls. The sound is kind
of cute in such a PW position, and I'd like to use it, so that is why this
'theremin effect' bothers 
me. Any suggestions on how to evade it?
4) There is also the problem with the pitch stabitilty - with the pots in
PW position, the pitch change is very obvious, though, when we have a
standard sqr and tri output, the entire output seems very stable in pitch..
Any thoughts on why this happens?
That's all I can remember for now...
thanx
smilen & T.J.