Hmm... A good indicator for answering your question is the time it takes until a former castle spot after collapsing is occupied again. And as far as I can see, that is the case instantly - in almost every case I know. And I traded about 10 DF-castles in the last 12 months. It took approx. 3 to 14 days until somebody bought it.
So my answer is: Yes, there are people who hear if a castle falls on DF - even in the woods. I hope, my answer was more polite than your intention was. But maybe I am wrong about your intentions. Anyways: Your reply was offtopic - and so is mine.
Let´s concentrate on business