Hi,
Try to find out which component is generating, it could also be a temperature effect of several components together.
Just adding a heatsink is usually not a good solution, what if the ambient temperature goes to 35C, like last week here in Amsterdam...
Does your heatsink method still work well then?
Maybe you have a power supply or opamp that has a too small Phase or Gain margin?
This is temperature dependent and can go wrong if you are on the edge.
Perhaps you are suffering from a mechanical failure component, that only occurs in a certain position of your device?
Kind regards,
Bram