Zoom H4N constant hum at 50Hz

["lamacchiacosta" lamacchiacosta]

Hello,

I just found that my Zoom H4N has a constant hum noise on the recordings at=
 50Hz.
I tested recording with the AA batteries and with an adapter I built to fee=
d the recorder with professional camera batteries.
Batteries in both cases and same hum noise either in the internal mic chann=
el and in the external XLR mic input.
When the input level is set at "75" the hum noise level is at -63dBu, prett=
y big though.

Has anyone got the same issue with that recorder?

Many thanks

Emanuele Costantini