I'm using SoX on Centos 7 to record the audio output from GQRX, a SDR application. I've selected Monitor of Built-in Audio Analog Stereo from the Recording Tab of the Pulseaudio Volume Control. I'm trying to save a .wav file with a sample rate of 6k. I'm using the command

sox -t pulseaudio 2 --rate 6k --channels 1 test.wav

This works and my test.wav is what I expect except that the duration of the file is about a third longer than the actual recording time. 3 hours and 15 minutes of recording time results in a file with a duration of 4 hours and 21 minutes.

I couldn't find anything online or in the SoX documentation concerning this. Is there something else I can try to make the wave the actual length of the recording?