In my experience this tends to be a lot more noticeable in the winter even on dry roads when tires and road are cold and road is sometimes covered with debris from winter salting or deteriorating pavement. It seems even minor bumps under these conditions will cause the regen to kick off whereas on a warm summer day it takes a lot worse road conditions to trigger the same...

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