Check if the CD source was selected immediately after connecting the power cord.
If power is connected to your product and then the CD source is selected, it's possible you might hear a pop. If this occurs, it should only happen the first time you select CD; it should not continue to happen unless power is disconnected and reconnected again. If you do experience this, you can avoid the pop by powering on the system to a different source (i.e. FM radio) after connecting power.