Self-flashing LED oscillates when in OFF state of cycle

[ResR]

I was testing two different self flicker LED's with a piezo element parallel to the LED with current limiting resistor to power supply to listen what sound it makes and I found out that L-56BSRD/B has odd oscillation when it is in off state, it sounded like two different frequencies - one short clicking sound 4 times per light cycle (clock signal?) and other was high pitch sound that turned off when the LED went on. Can anyone check this with an oscillator and can it cause interference to other microcontrollers? Could it have a built in microcontroller? I always thought it had something easier like astable transistor oscillator in IC form until now.

[amyk]

I remember reading somewhere that flickering LEDs may use the same chips as in musical greeting cards, so you may hear a familiar tune from them, although if you don't hear anything recognisable it could be that they use the defective ones which still have some sort of output.

[Zero999]

The part number he gave is just a normal flashing LED.
http://www.farnell.com/datasheets/1864128.pdf

It could be a number of things which is causing this. The astable multivibrator inside the LED probably runs at a much higher frequency, than the flash rate and is divided down. It's possible the peizo is oscillating because of some non-linear effect inside the LED. Perhaps removing the piezo and looking at the waveform on an oscilloscope would provide a more clear picture.