I see it was "noise" you were talking about.  I am a physicist, and in the field, noise is the word used to describe any random fluctuations that affect a measurement.  We spend a lot of time trying to understand the sources of these fluctuations, whether they arise from thermodynamics for example, and are thus fundamental, or if they are dependent on the way we have done things.  Sorry for throwing in the physics language. When I see problems like this, the physicist in me takes over my thought processes.

Best,

Harvey