Things to take into consideration when thinking about your recording environment.
Unbalanced connections. if your using an unbalanced connecter like for instance a mic with out XLR input OR TRS (tip ring sleve jack)
you will get interference from radio waves into your signal.. the way a balanced connector works is by sending two signals from the same
source but with one phase inverted to cancel each other but then at the receiving source the signal gets flipped back so you get twice the signal and no sound or electrical distortion or interference
Listen to your room. Sit quietly in your environment and just listen try to determine what you can hear around you if you notice anything
you can sure bet it will turn up on your recording with a condenser, and maybe if you have an ultra sensitive dynamic.
Equipment make sure you service it regularly, check each individual piece starting from the input source. Faulty mics cause noise, faulty cables, speaker amps cause noise, faulty pre amps cause noise specially if its valve driver, and monitors close to sources cause noise
Learn about every bit of gear you own and learn about every inch of your environment, every corner that can trap low frequency's, every reflective surface for high frequency's to bounce of if you can acoustic tile these surfaces to shape your room sound to stop fatigue on you and your listener.