They were a service bulletin item. If you're sure the noise only happens with the A/C on, I'm not sure how they could be the culprit - if there's water in there, it'll be in there all the time. But it's probably still a good idea to have them done anyway as you really don't want to deal with replacing the blower motor controller/resistors if they get wet.
Yeah, it's only when the AC is on.
Another interesting note, the noise is louder on higher ac settings. You can hear it at 1, but its louder at 3.