IIRC the 2.4GHz band has 13 channels. of which only 1,6 and 11 are not overlapped. If you have neighbours with wifi enabled devices close by their devices will interfere with your signal.
It may be as simple as changing your channel, or have you already tried this?
In any event, I would download and install the following and look at the traffic in your area. inSSIDer – Discover The Wi-Fi Around You | MetaGeek
Setting your router to the channel that has the least amount of traffic will be a good starting point.