While I believe in spirits, you should try and rule out any logical explanations first to make sure there's nothing wrong. Sounds could be a house settling, or perhaps a broken pipe that needs fixing. Seeing dark shadows could mean a problem with your eyes, or perhaps an inaudible sound. Studies have shown certain frequencies we humans cannot 'hear' can still effect us by causing hallucinations, even make the hairs on the back of your neck stand up [some horror movies have been known to use these sounds in their soundtracks] this noise is usually caused by old fans in cooling/heating units.
How to see spirits better there's a few ways, through meditation and chakra work you can increase your spiritual connection. There's a few exercises people say increases your 'psychic abilities' you could also look into. There's also a theory that our ability to see spirits diminishes as we age because our eyes weaken, hence why children see more spirits than adults.