Well I would try and 'half-split' the symptom to try and determine if the noise generator input is effecting the analog input A/D conversion, or if the noise generator is effecting your temp sensor. Why don't you disconnect the temp sensor and instead jumper a wire from the 3.3v pin to the analog input pin that was reading the temp sensor. Then run your program without the noise signal input to verify a steady 3.3v reading and then input the noise source and see if the 3.3v signal is effected or not. That might give one a direction to go from there.
DEFAULT: the default analog reference of 5 volts (on 5V Arduino boards) or 3.3 volts (on 3.3V Arduino boards)
Good thinking MarkT, thanks!I notice that when the microphone picks up a signal, the supply voltage goes from 4.99V to 4.98V, this problem happens when the opamp gives an output, it effects the supply.Just removed the opamp, and the problem's gone!What should I do? =/