Most people interpret Wi-Fi interference as a bad thing but don't worry it isn't always bad. The most common cause of Wi-Fi interference is poor craftsmanship when installing routers and antennas. Metal walls, metal objects in the room, or even water piping can change the shape of an antenna's radiation pattern shortening its effective range.
Frequent Interference Problems:
People who have a wireless router in a room with metal walls, or adjacent to an air conditioning unit, often complain about the wireless signal being disrupted. The reason for this is due to the powerful magnetic field created by these appliances which usually interfere with the shape of the antenna's radiation pattern. In turn, this decreases the range of the wireless signal.

Is it bad to have your router in a metal room?

It can be very difficult to install your Router in a metal room without interference. The best idea is to move it away from metal objects or turn off appliances that generate magnetic fields when they are close to the router. It all depends on what has priority, good performance (longer distance) or less Wi-fi interference (stronger signals). If you have no choice but to keep your router in a metallic environment I recommend buying high gain antennas which can increase the reach of your wifi signal while being affected by metal objects or waves generated by other devices.

Separate Wireless Networks in Your Own Home

If you have numerous wireless networks in your home that are linked to separate devices, this can be more inconvenient than your neighbor's network. We recommend creating a guest network on the same router or access point as the main network with its distinct network name (SSID). This way you can give guests internet access without having to provide them with the password of your main network. 
What causes wireless interference?
Many devices cause wireless interference, such as cordless phones, Bluetooth speakers, even microwaves. All these devices can be used simultaneously with no impact on performance or speed unless they operate within the same frequency range (2.4 GHz). Cordless phones and cheaply made Bluetooth speakers usually operate in 2.4GHz which is the same band as Wi-fi so don't connect both your router and the Bluetooth speaker to the same plug.
Also, to avoid interference with cheaply made Bluetooth speakers or headphones we recommend using 5GHz wireless networks as most of them are dual-band. Cheaply made devices usually operate in 2.4 GHz so if you have no choice but use them on a dual-band network keep them away from the main router at all times. If possible buy quality devices which can communicate in both bands (2.4 & 5 GHz) this way they will work more efficiently without sacrificing anything regarding performance or speed.

Physical Obstacles to the Wi-Fi Signals

Obstacles that are easy to eliminate include trees, walls, and fences. In some circumstances, you may be able to relocate the access point away from the problems. The housing construction materials are more difficult to manage. In such instances, a mesh network of numerous wireless access points that can go around the obstacles is advised.

The best way to combat this issue is to keep your router away from high voltage lines, roads, sidewalks, and other electrical appliances. Ensure that no one can tamper with the antennas of your wireless router as this may also affect its range significantly.
If you are using multiple access points throughout your home or office ensure they are not on the same channel (channel 6 or 11) to avoid interference between networks. If some areas of your house have a weak signal while others do not, try changing some of them to another channel.