Heat sinks do that. Just brush them with lightly with your hand and you will hear a ringing (brush anything with your hand and you will hear something). Your hearing is extremely sensitive and I doubt you can hear this above even quiet music from across the room.
This has no affect on the audio signals amplified by the amp. In order for metal vibration to induce current flow in metal there must be a strong magnetic field in the vicinity (Maxwell's equations). For example hysteresis will cause tranformers to vibrate and by logical extension transformer vibration will incude a very small voltage signal in a transformer (note by small voltage I mean extremely small becuase a transformer winding is of low resistance and therefore something extremely unlikely to get through the power supply circuitry to th eaudio signal chain)
This has no affect on the audio signals amplified by the amp. In order for metal vibration to induce current flow in metal there must be a strong magnetic field in the vicinity (Maxwell's equations). For example hysteresis will cause tranformers to vibrate and by logical extension transformer vibration will incude a very small voltage signal in a transformer (note by small voltage I mean extremely small becuase a transformer winding is of low resistance and therefore something extremely unlikely to get through the power supply circuitry to th eaudio signal chain)