A group of PCs is bound to stay in a noisy location for some time, with a noise level and/or type which would normally prohibit sleeping, such as sudden, short bursts of noise (e.g. gun fire, loud vehicles).
Could characters capable of accessing Virtual Reality use this to block the noise and get sleep? I am aware that this would make them prone to sneak attacks, but implementing some wake-up pulse from inside the Matrix using a PAN-attached device seems quite possible to me.