Part Number:LMZM33602
Our PCB contractor has had some quality issues and we are trying to debug a problem that seems to center around the LMZM33602 on our boards.
(note that the PGOOD signal is pulled up to 3V3 with a 10k ohm resistor elsewhere on the schematic)
On several of these boards, the issue manifests as a high pitched (I assume 5.1-5.6 kHz, for reasons detailed below) whine coming from the chip along with non-stable output voltage.
The waveform below shows PGOOD (CH1) and VOUT (CH2) 
Any ideas on what could be the issue? Our problem boards have this behavior, although for some the frequency reaches as high as 5.6 kHz and VOUT actually gets as high as desired (12V) though it still experiences rising and falling in sync with the PGOOD (which always looks identical to the above waveform).