Interference on ADC reading (STM32F4)
All DACs require a voltage or current reference. The reference can be supplied by an external chip, or be built-in to the DAC. 

Here is one thing you should check: Is your reference oscillating?

Causes of reference oscillation include:


not using a filter capacitor that a manufacturer recommends on the reference output of DACs with built-in references  

1.1 not using a filter capacitor that a manufacturer recommends on a external reference output
using a filter capacitor with the wrong ESR (Equivalent Series Resistance)- consult the data-sheet of the reference
oscillation in an op-amp circuit which "buffers" the reference due to capacitive loading or design error.  

3.1 Not using an op-amp "buffer" circuit when one is required. Are you drawing too much current from the reference?
Excessive noise on any power supply (try powering up your circuit from the appropriate combination of batteries)


It does not look like a digital interference problem because the disturbance seems to be very steady, and there are no "spikes" or other discontinuities in the waveform. To be sure, please measure the frequency of the disturbance and find interference that varies at the same frequency or an i/o port read or write that occurs at the same frequency