XCTrack contains a "Weak lift indication" feature. If you fall down in calm air by 0.9 - 1m/s but, while flying, you are only falling down by 0.2 m/s, this means you are flying in air mass going up... This is indicated by the double beep vario sound. you can disable it by turning off the "Weak lift Indication volume" in Menu/Preferences/Sound/Acoustic Vario.
Read more details about settings in Menu/Preferences/Sound/Acoustic vario
Watch this short video regarding the weak lift vario sound