I have had the timing belt & tensioner replaced about 40k miles ago. The belt actually broke while driving, but since its a non-interference engine, the mechanic said all was fine.
It might be worth mentioning that the noise goes away when I just lube the center of the pulley as well, not just behind it. I can't see the center of it simply because its so close to the radiator, but it feels like there is a nut in there holding the pulley on. If I lube around the nut, the sound goes away.
I should also point out that I have been dealing with this issue for about 2 years now. (Started long after the timing belt change). I drive it nearly every day. It still runs perfect and doesn't seem to be getting any worse. Its just annoying. I'll lube it and the sound goes away for 2-3 weeks and then comes back.
I've found that this type of lube works best and lasts longest: