Re: power supply noise
What is your board layout like? It is best to build switching power supplies on a single sheet of copper clad board with the component leads as short as possible.
If you have long wires, you will get noise from the switcher itself, get noise induced from your car, noise from Radio Moscow etc etc....
Is the circuit quiet when powered from a bench power supply? this will help tie down where the noise is coming from..
Use good quality capacitors as well (tants)