Many high frequency transient spikes will go right through the regulator. A .1 or even .01 uF capacitor will help, but a series chip choke type inductor will give you the best gain for the money. I have been working with switching regulators for battery boost, and they were reeking havoc with a RF receiver built into the app.. I isolated the regulator circuit using a chip inductor on B+ and tied the grounds together through another chip inductor. The high frequency noise dropped by a factor of almost 20. It meant 800 foot range as opposed to 200.