Applies to: All products
It is normal behaviour to still be able to hear some signal from your mic, even when the gain dial is set to the minimum position, as there will still be some gain being applied.
The preamp gain dials are not like faders on a mixing desk, which will mute the signal completely at the minimum setting. To cut the signal, you have to mute the input on the next device in the chain (for example, the track you're recording onto in your DAW) or disconnect the mic.
The amount of gain applied to the signal at the minimum position will differ depending on the specific product you have.