Plantronics M55 Bluetooth headset too loud with iPhone 5

Hello,

I bought a Plantronics M55 Bluetooth headset for my iPhone 5.

Unfortunately, it is so that even if the volume is turned all the way down, the calls are too loud and sometimes overridden. When listening to music that is not so. Not even with the original Apple headset.

Have the M55 tried it out on my old SonyErricson because I hear the conversations as clear and not overloaded or too loud.

Someone might know a hidden setting?

Otherwise, I have to try another headset.

regards

Thorsten