Apparating/Disapparating

[karenlyall666]

No: HPFGUIDX 110416

I searched the archives and could find nothing on this question, so I 
apologise if it has already been covered to death.

Can someone please help me understand how Dumbledore's original 
arrival in Private Drive was silent, when all other cases of 
apparition/disapparition is heralded by a noise?

UK PS PB p12
" A man appeared on the corner the cat had been watching, appeared so 
suddenly and silently you'd have thought he'd just popped out of the 
ground."

UK GOF PB p114
"..., he disapparated with a small pop."

And although I don't have OOTP to hand I recall all instances of 
Mundungus or the Weasley twins apparating/disapparating to be 
heralded by a resounding crack.

Any ideas anyone

Karenlyall666