RC snubber

My final recommendation to the customer was to put in a small RC snubber very close to the IC between its SW and GND pins. Typical values of this snubber are 470pF to 4.7nF and 10Q to 100Q. Note that since this Band-Aid fix is very layout and parasitic dependent, I usually ask the customer to try all the corner combinations first, such as 470pF/10Q, 470pF/100Q, and so on. The customer may also need to play with intermediate R and C values to optimize performance and not take too big a hit in efficiency in the process. I know the Japanese customer evaluated the snubber fix at his end and went into full production with it. 

A clue provided by the customer is that a ceramic cap from SW to ground helps. So yes, noise is also an issue here. Hearing this, I would have immediately suggested a PCB layout review, and if necessary a small RC snubber (lOQ to lOOQ in series with a 470pF to 4.7nF capacitor) between SW node and ground. The advantage of an RC snubber instead of just a C is that the energy in the capacitor is dumped in the R of the RC snubber, not in the switch. 

In some cases the transmitted pressure signal is so noisy that a snubber may be required. For electronics an RC filter may be used. 

---