Background Histogram Peak(s), what to know?

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Hello! I am new to METROTOM OS and CT Scanning. My background is in mainly CMM Programming. I have a quick question about what to expect for background (air) grayscale peaks in the METROTOM OS histogram. I am currently seeing 2 distinct peaks that are widely spread and my instinct is that there should be only a single peak representing the background on the detector. The system is a METROTOM 800 225 kV system, I have recently performed all calibrations through METROTOM OS (detector, geometry, and axis), and I ensured there is nothing between the emitter and detector that may be the cause of the second peak. 

I attached a photo of what I see in the histogram with no object in the beam path.

Is this behavior normal? And if not, what has been/has to be done to correct this?

Thank you for any assistance!