Low noise, high voltage resistors
Metal film resistors work best for lower 1/f noise.  1/f noise arises through the interaction of the carriers with grain boundaries in the bulk material.  A metal film is less likely to have distinct carrier disruptions at crystal boundaries (depending upon the allotype).  However, metal film resistors can have inductance, depending upon how they are made and this may not work for you.  Keep in mind that a 10 MOhm resistor may have significant Johnston noise.