Another source of noise is, frequently, the power supply unit;
Problems can cause noise:
(bad) grounding
low voltage
low current capability (this is, the unit drais/need 500 mA and you use a 300mA rated unit
DC current not filtered

Make an experience: Try using your device powered by the power supply unit you have and than change the power supply by batteries (full charged, correct voltage, correct current); any difference?

Finally, I am trying to change all my power supply units by the new concept power units: the "switching" power supply units (nowadays, all the cell phones chargers are switching, for example).
Advantages are: they are small, light, and the noise, if any, is very high frequency (not 60Hz or so), that is, not audible.


regards, from Brazil
Luiz Dias
Watch the videos of me playing the percussion/conga drums with a great band!
--> http://uk.youtube.com/user/footkeys