'90 80Q, strange noise (chipmunks??)

[Jim Vienneau]

I have a 1990 80Q with 120K on it. Lately it has started to make a
(chirping, ringing, pinging, chikmunks in a blender) kind of noise. It
will only do it under load and only after it's warmed-up. It almost
sounds like the exhaust rattling but everything seems tight. I'm just
looking for any ideas on what it might be? Anyone been here before and
figured it out?

Thanks, Jim