What senior Sifu said

Those areas where there are lots of bird shits below them with external sound playing will have little chance of nests but those playing with internal sound tweeters will eventually resulted in nests.

First there will be bird shit and soon, about two to three months or so you will start seeing some feathers on the spot.

The moment the feathers are on the floor you will soon find that there will be some kind of nest markings above the spot.

If you are lucky the marking will eventually turned into nest.

The nest making process is nearly the same and you will see this over and over again.

Remember, the chance of having nests is higher if the birdshit is found below the internal sound tweeters as compared to external sound tweeter.
There must be some reason for this but i know for the fact that the internal sound are usually played much longer as compared to the external sound.