There's no noise floor with digital recording. We shouldn't confuse ambient noise (picked up by a mic) with tape hiss (built in to the recording medium, nothing to do with mics).

Background noise (i.e. a fridge hum or battery hum or wind rattling a window) does not get quieter or louder relative to the record level. Changing the recording level doesn't magically make microphones quieten a car outside.

The only thing that will alter that is how close your mic is to your guitar or voice.