One of the more interesting sounds I've noticed is after backing out of my driveway (by this time the ICE has started and is not yet warmed up) and moderately accelerating down the street, for the first 15 or so mph the engine stays at idle for the most part while the battery drives the system. It's kind of interesting to drive away while you can hear the engine just idling.

Two climate control systems, one inside and the other at the tailpipe.

2007 Camry Hybrid (in service June 2006)
FE: 6.67L/100km or 35.3 mpg (6.11L/100km or 38.5 mpg in summer)