I noticed this too. I'm still trying to decide if the reason it's noticeable is because it's in a garage which echos the noise and the engine is not running as I've not noticed it anywhere else.

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

2007 Camry Hybrid (in service June 2006)
FE: 6.77L/100km (34.8 mpg) over 37750km (23450mi)
75% city - Ave trip 20 min - 2 Winters