As the BBC like to remind us whenever they go to the highlights on match of the day what a fantastic atmosphere those 38 people and a drum create, is that part of the problem. The constant droning which is the same wherever is happening on the pitch itself cant have a good effect on the players. In normal grounds the atmosphere ramps up as the players perform and gives them the boost they need. Likewise when the players are not performing a burst of atmosphere may help them raise their game. This doesn't happen at Selhurst, for the players it must be like listening to distant roadworks while at work and you cannot wait until clocking off time to be able to gert away from the drone.
I can imagine these being a tad distracting also