Plantronics M2500 - beep codes

My new M2500 headset works fine................

Does anyone know what the different 'beeps' mean with this headset.

Nothiing in the 'skimpy' manual.

I seem to get a 'low' tone for loss of signal, then a 'high' tone when a
signal is restored.

I also get a 'low/high' combination even with a good signal.

Headset has been paired with a V600 and a T610 - same beeps.