New Post: Wasapi Loopback Recording -> Heavy noise/distortion

You do need to get the right WaveFormat - using the one from capture should be OK, although WASAPI annoyingly likes to use WAVEFORMATEXTENSIBLE, so often I turn that into the equivalent PCM or IEEE Float WAVEFORMAT.

You might simplify things by removing the creation of another thread.

I'd also look at the WAV file you make in an editor like Audacity and see if there is anything visually obviously wrong with the waveform. That can often provide clues.