Hello Michael,
The Ground on the full wave bridge and the ground on the 2N3904 should not hooked up the way your schmatic shows it.

It is much better to keep everything with only one ground point. The one on the full wave bridge would be acceptable.

The other ground reference (on emitter of 2N3904 and Anode of diode) will be at a different voltage levels (especially during the cross over points of the Alternating Current signal) and ground loop current(s) will flow between them.

The typical way to get a line frequency reference without these nasty ground loops is to use capacitive coupling or optical isolations.

Regards,

Charles Bannister