Just out of curiosity I tried the Rev 1 source again this morning, on a separate breadboard. The tone was gone — but it was picking up crosstalk from the adjacent breadboard circuit I’d connected to for power. I tried adding a 47 µF cap from base to ground and the crosstalk went away.
Looking at it some more I think I do like the Rev 1 source better — with the 47 µF added.