CZ 7A Pro threshold?

Owner's manual states "Note: In the AUTOTUNE mode, you will hear a slight "threshold" hum at maximum sensitivity but not of settings at 8 and lower."
Then the machine is "silent search" when operating in AUTOTUNE with sensitivity below 8? Can that be right? What am I missing, or not understanding? I used a CZ5 for a couple of years on salt beaches and appreciated the break, or waver, in the threshold on deeper targets. I would appreciate any feedback that could explain this to me. Thank you.

Lonnie...... owners manual is correct. Sens must be on maximum....... in order to hear a slight threshold 'hum' ......whilst in AutoTune (All Metal) Mode. Same with all other CZ's. You will only hear a threshold 'hum' when Sens is set to max (or very near max) whilst in AutoTune. On a analog CZ....... Sens 9 or 10 will give you a slight audible 'hum'. If you drop Sens down to '8' on a analog CZ........ the threshold hum is gone. Keep in mind...... this applies ONLY to the All Metal Mode!!!

Thank you. Much appreciated.