bjt - Lots of noise in the microphone amplifier circuit when idle

I come again to get help from the experts.

I am using this BJT transistor in the circuit.

http://www.fairchildsemi.com/ds/2N/2N3904.pdf

Here is the microphone that I am hooking up in the circuit.

It's an electret condenser microphone from digikey.

http://www.cui.com/product/resource/cma-4544pf-w.pdf

Here is my design

I am following the tutorial from this link to build the amplifier. It's exactly the same circuit but with different values to make it work with microcontroller. For that, I have used the supply voltage of 5V instead of 9V as in the tutorial. I have also tweaked the values of resistors to make the correct biased voltage.

http://www.youtube.com/watch?v=Br3uOM0IVjc

The problem is that I get a lot of noise. I checked with oscillosope and it is biased correctly, i.e., midway between the 5V. But you can see a very noisy signal. I hooked the circuit to a computer speaker and you can hear the noise after you hook up the circuit. The output works correctly though, i.e, when you play a sound in the microphone you can hear clearly in the speaker but during idle there is a noise that is audible.

What is the reason of this noise and how to minimize it while the microphone is sitting idle? Thank you for the help.

Answer

The noise is very unlikely to be coming from any of the components in the circuit. The biggest culprit is likely to be the power supply. Add a 22uF and 0.1 uF (helps with high frequencies) capacitor and a 100 ohm resistor that feed the electret part of the circuit and a 22uF across the 5V supply.