Dick, I had a similar problem both because of the loudness and the fact that the
indicator on the dash was hard to see during the day.

This may be easy or difficult depending on your vehicle (which I know zilch
about) but was simple on mine.
I got a piezo buzzer from Radio Shack for a few bucks. Has pigtail leads. Pull
the flasher unit and run the leads through holes that are typically in the
contacts. Observe polarity! (You may need to look up wiring to see how to
connect it.) Insert flasher. The buzzer will sound when the turn signal is "on"
and the turn lamp itself is off.
Mine was too loud, so I put some tape over it to quiet it down. I just let it
hang by the wires, as it's very light.