Sample rate changing audio pitch I am using rtl-sdr at an adjustable sample rate to get stuff from a WBFM radio station.  I then filter and demodulate it.  When I sample at 2.4Msps, the sound is 'choppy'.  I tied the sample rate to a slider on gnuradio, so I can vary the software radio sample rate by moving around the slider.  It turns out the pitch of the person talking/singing's voice gets lower as I move the sample rate down, and higher as I move the sample rate up.

Why?  2.4 million samples / second is much greater than 2*20,000Hz.  Why would there be a difference between sampling at 2.4 and 2.8 Msps?  All the frequency content is already covered in both cases...

Also: in gnuradio I can adjust the width of the low pass filter that is placed before the FM demodulator.  I thought that making the filter very narrow would remove the high frequency content of the audio.  Well, it doesn't.  It just makes the sound 'staticy'.  Why?
A couple of things jump out when looking at your diagram:


The first low-pass filter has a decimation of 4, so the sampling rate at its output is 256 kHz. However, you have set the sampling rate of the FM receiver and the second LPF to 224 kHz. These should be 256 kHz.
The cut-off frequency of the first LPF is 150 kHz. This means a total passband of 300 kHz. This is larger than necessary, so you'll end up picking up more noise than the optimum.
You multiply the audio output by a constant factor of 2. This may be too little, or too much. I'd suggest using a slider to control the volume. If you connect a scope sink to the audio sink input, you'll be able to easily get the optimum gain: you want the signal to be withing [1,-1].