Your computer's motherboard is also working in the "Gigahertz" spectrum. That "noise" is being picked up by your built-in Wi-Fi transmitter. Unfortunately, the higher that noise is, the more likely it is for your wireless adapter to lower bandwidth automatically (by lowering the link-rate and avoiding frequency interferences). As CPUs these days clock dynamically, the Wi-Fi adapter needs to constantly adapt the link rate which not only causes a variation in Mbps but may also be the cause for dropped connections. Especially on laptops, the Wi-Fi adapter is often built close to the memory and CPU bus, which is a major source for problems.

Of course, this all depends on the design of your Wi-Fi adapter, but if these symptoms sound familiar you might solve this issue by getting an external adapter. Some of these adapters, such as my Linksys adapter, even have a little stand that's connected via a long USB cable. Putting that kind of space between the Wi-Fi adapter and your CPUs noise is likely to help a lot. Of course, that's not too handy when you're traveling, but at home it's a viable option. Typical Wi-Fi adapters such as the Linksys AE2500 (802.11n dualband) or the MSI will set you back between $20 and $40 and they're worth every penny.

An easy, yet often forgotten piece of advice: Make sure that your router's firmware is up-to-date -- especially if you've purchased a new one. Expect bandwidth, feature set and resiliency to signals to increase with the first few firmware updates. (My Linksys router could only deliver full bandwidth to my living room after the upgrade.)