Unfortunately the default librtaudio-dev library on the apt is outdated and falsely configured. Therefore you most probably will experience audio problems on linux mint. There is a fix but it requires a bit of manual work for you to do.

You need to clone the repo for a manual install of rtaudio. git clone https://github.com/thestk/rtaudio && cd rtaudio
Create a build folder and cd into it. mkdir build && cd build
Cmake the project without alsa support cause that is what actually breaks it . cmake -DCMAKE_INSTALL_PREFIX:PATH="/usr" -DRTAUDIO_API_JACK=OFF -DRTAUDIO_API_ALSA=OFF ..
Remove the outdated dependency. apt remove librtaudio-dev or your rtaudio version
Install the new dependency sudo make install
Done! Start Sdrpp and enjoy clear sound.
Thanks to cropinghigh for the cmakeflag.