6400 Preselector Band Limits?

I have a new FLEX-6400, no ATU, no GPSDO. Spending time learning the receiver and reading the manuals. I am running it on the Mac mini (Late 2014) with a local network connection. This is my entry into SDRs for Amateur Radio.

Tuning the receiver using one pan adapter and one slice receiver, I hear a click from inside the radio, and a change in the sound of the noise. Tuning in the opposite direction, I hear the click and back to the first sound of the noise at a different, but nearby, frequency. I suspect this is switching in the "optional" preselector. The manual (12.2.1) calls it optional, but since it is not a choice at purchase, I suspect is sometimes bypassed.

What are the Frequency Ranges of the Preselector? What ranges are simply Bypassed (if any)?

So far, the more I learn about operating this radio, the better I like it.

Tim, KI4TG