This is often a difficult problem to solve, but it could be any interfering source on 2.4GHz. I've had issues in the past with wireless speakers and phones that slowed my computer network. Also, try different areas of the room to see if there is a dead spot in part of the room.
I'd also take a quick look at my router QoS settings to insure that gaming is set to high priority.
I have a 2.4GHZ coordless phone sitting right beside me....
I actually had a real techfest day today. My GF is away on a Spring break trip so I upgraded the home phone system to a Panasonic 1.9GHz DECT 6.0 - 5 phone set to reduce interference today, also went to HD cable and 50Mbps (from 3Mbps) Internet. What a day!
I noticed that with the 2.4GHz wireless headset and speakers, and phone nearby in my bedroom my wireless speeds there were down from before those interference sources -- might be worth checking for you too.