Routers work using high-frequency radio signals. Like all radio signals, it's possible for them to pick up interference.
This can be caused by all manner of electrical appliances, including; microwave ovens, security cameras, Bluetooth devices, cordless phones and baby monitors.
To avoid interference, try and keep your router away from the above devices if possible, or ask a retailer specifically for devices that operate on a different frequency.
Wireless interference can also be caused by neighboring wireless networks. In South Africa, there are 13 wireless 'channels' which routers can utilize, each representing a slightly different frequency. Many modern routers will automatically detect the least congested channel and use that.
If you're experiencing issues, you can check whether your router could perform better on a different channel. This can be easily done using a tool such as inSSIDer. Please note that these are third-party applications and not 'officially' endorsed by Pindrop.
If you can see that your router is operating on a congested channel, you can try changing this through the router interface. We generally find that the least congested channels are 1, 6, and 11.