I promise it hasn't just started today, you may have just noticed it today and it will be more noticeable as the nest is getting bigger. I don't recommend tackling it yourself unless it is at a height where you can reach without going up a ladder, you are going to need a fast escape route. there are a few products on the market but whatever you use follow instructions and do it late at night when they are sleepy.
I charge �25.00 for such a nest but I know others charge up to �35.00. Good luck