Grandstram GXW4004 & GXW4104 strange noise on tansfer

[AldoLinares]

I am trying to figure out what it's making this sound when someone does a transfer, it has to be with the GXW4104 because it happen with voip phones and with FXS phones connected to 4004.

The noice happen exactly when you get the transfer.

Its like a crackling sound.

Anybody experience the same?

Thanks