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LMZ22008 Audible noise

Other Parts Discussed in Thread: LMZ22008, LMZ22005, LMZ22003, TPS62130, TPS84A20

Dear Sir/Madam,

I am using various Simple switcher parts:

2x LMZ22008 (master/slave) +1V0
1x LMZ22005 +1V5
1x LMZ22003 +1V8
1x LMZ22003 +2V5
1x LMZ22008 +3V3 
1x TPS62130 +3V6

There is audible noise coming from what appears to be the LMZ22008 used on the +3V3 supply.
Each supply has a ferrite bead and filter capacitors on the +12V input side.
The layout, schematic and input/output capacitors are in accordance with the datasheet.

Before i start isolating each supply and running load tests are there any pointers on what could
cause this type of instability.

I can provide layout and schematic information.

Regards Grant