I didn't really like the original sounds when pressing and release the radio button. That's why I've adapted two other soundfiles. The result for me is a little more natural and acoustically better to classify whether the radio call has started or ended.
Simply copy the two files to the following folder: DCS-SimpleRadio-Standalone\AudioEffects
First save the originals!
Update: Added subfolders for different volumes. I prefer the -20dB Soundfiles, while using in SRS the Speaker Boost with 24dB. It's individuel! Test it out!