There can be several potential causes for strange sounds heard outside your bedroom while you're asleep. Here are a few possibilities:
Environmental factors: Some natural occurrences or environmental factors can produce unusual sounds. For example, strong winds can cause objects to move or rub against each other, resulting in strange noises. Similarly, falling branches or debris can create unexpected sounds.
Animals or insects: Nocturnal animals or insects can be active during the night and produce sounds that may seem strange or unfamiliar. Creatures like owls, raccoons, or even small rodents can generate noises while moving around or communicating with each other.
Plumbing or household systems: The sounds you're hearing might originate from within your own house. Plumbing systems, such as pipes or water heaters, can sometimes create noises when they're malfunctioning or experiencing pressure changes. HVAC systems or appliances like refrigerators may also produce odd sounds.
Neighbors or outside activity: If the sounds are coming from neighboring houses or apartments, it could be due to activities or appliances used by the occupants. Loud music, home renovations, or even a washing machine on a high spin cycle can generate sounds that carry into your bedroom.
Mechanical or electrical issues: Some mechanical or electrical components in your home or the surrounding area might be malfunctioning. Faulty equipment, loose wires, or malfunctioning electrical transformers can lead to unusual sounds.
Weather-related phenomena: Certain weather conditions can cause sounds that you might perceive as strange. For instance, thunderstorms can produce thunder, lightning, and strong gusts of wind, resulting in various noises.
Psychological factors: It's also worth considering that the sounds you hear may be subjective and not actually exist outside of your perception. Hypnagogic hallucinations, a condition that can occur during the transitional states between wakefulness and sleep, might lead to the perception of sounds that aren't present in reality.
If the sounds persist and cause concern or disruption to your sleep, it may be helpful to investigate further by checking your surroundings or consulting with professionals, such as a plumber or an electrician, to rule out any potential issues.