Alternatively, since there are sound notifications upon finishing buildings, technologies and units, playing with sound should do. Problem is, those notifications are in the same category Action as selection sounds and voices, which are much more repetitive, so I'm working on turning down Gain to 0.1 for the latter.
I also found that RandGain must be 0 for the change to take effect.
0 exp in modding, but here we go..