Yes, I'd personally bet on wireless internet, especially if it's close to either the WAP or the computer (or some other wireless device like a Nintendo DS, iPod Touch, etc). But there are a lot of radio sources in any modern house. And with unlicensed radio devices such as this, there's no solution. The FCC's rules on unlicensed stuff is "if you interfere with a licensed operator, you have to shut your equipment off. But if anything else interferes with you, tough titties." Really, that's about all they can say. If it's your own stuff that's causing the trouble, it's possible you could physically move it or maybe change the channel that your wireless is working on.

First thing though is to confirm that it's interference. Then while you're sitting there watching it getting interfered with, try turning off all the wireless devices including your WAP. Of course, if you're very close to a neighbor with a WAP (like, in an apartment) it could be theirs causing the trouble. You really have no recourse if that's the case. I suppose you could cover the wall between your place and the neighbor's with aluminum foil, but that would probably just make you look like a nutter.