Depends on the property (and of occupancy of the hotel). At Hilton Phuket Arcadia in the Lotus Wing it is a terrible problem; the connecting door is right next to the bed. (Great work, designer). You can hear everything including telephone rings, talking, coughs at night, toilet doors banging etc. I am not a light sleeper but earplugs are essential for me at that property.

This is one of the reasons the better properties often filter Diamonds into corner rooms if available - only one neighbour banging about, and often a bit more room to play with, better view, more natural light etc.