PDM microphone issues - how to debug

[Bill]

Not sure where the problem is. Some of my boards, the microphone works fine, on others it doesn't. I am using a Knowles SPK0641HT4H-1 PDM microphone. I am using it as mono. On the failing boards, I have to same output from recording 1s of audio. The good boards look fine but the failing boards all have this waveform. Can anyone tell me more about the failure by looking at it? It is likely a hardware issue since it works fine on other boards. The PDM peripheral doesn't give me much in the way of debugging options.

[Bill]

Its 16000 int16 values of raw values from the PDM peripheral, mono, leftrising, 1Mhz, max amplification. 1 second of audio. 

[Kenneth]

I suggest to connect a logic analyzer to the DATA, CLOCK, SELECT, and VDD line and look at differences in timing (e.g. clock) when failing and working.