Hi, Anand. Printed circuit board isolation is usually achieved satisfactorily with overall isolation of the component that the circuit board is mounted in, e.g., Tenderfeet under the component and maybe a SuperSonic Stabilizer or two on top.
Additional component damping can be achieved internally with rope caulk like Mortite (available at hardware stores) and Permatex Blue RTV Silicone Gasket Maker (available at auto parts stores). Either or both of these can be used to damp PC boards, used sparingly. Grungebuster material is quite effective for internal damping, also.
You don't want to use rubber, Sorbothane, or other sonic "trade-off" damping materials with audio components or associated electronics.
Isolating washing machines and refrigerators and anything else in the house does not isolate audio or electronic components, which must be accomplished at the components themselves. Besides a myriad of other micro-vibrational sources, audio components themselves generate micro-vibrations and should be isolated individually to bring out more of their inherent potential.
You don't want to use rubber, Sorbothane, or other sonic "trade-off" damping materials with audio and video components. Dual rubber standoffs would be great for a refrigerator or washing machine, but not a PC board.
Vibrations generated by a mechanical device like a washing machine will transmit vibrations via the floor and walls, but the nature of the vibrations affecting the audio system will be determined by the materials the vibrations pass through along the way. The wood, joists, structural framework will characterize the vibrations. Vibrations reaching the audio components must be blocked or absorbed by materials and physics that are specifically effective with audio and deliver a sonically neutral end result.
Herbie's Audio Lab