<VV> Loud noise when hot

[Ron]

I have a run-down '66 sedan with a 110 engine I'm trying to get running well enough to sell for 500 or something like that.  It presently develops a loud noise, more like a screech than a knock, when it gets up to temperature.  It seems to develop good power otherwise.  Since the sound seems to come from the right side I pulled the right head today and can find nothing wrong except for one cracked exhaust donut.  I can't believe that a leaky donut could make that much noise, however, and wonder if there might be a problem with a rod, or, could it be a head gasket that leaks only when hot?  The compression is good when tested cold and the head seemed to have been torqued down OK..  Any experience on something like this?

Thanks in advance,
RonH