Samsung WEP200 headset noisy

Hi I bought a Samsung WEP200 headset and when in my ear and not in a
call I hear a high pitch noise. When in a call I cannot hear this noise
(possibly it is shadowed by the conversation).

Is it normal to hear a noise when not in use?

A bit history:
I bought it from Hong Kong
I charged it for about 5 min and then the charger blew.
I used it for without any problems.
Then I replaced the charger with another Samsung charger and recharged
it and then the noise showed up
Is it possible the noise did not show at first because the battery was
not fully charged?
What could be the problem?

Thx