We took a number 19 bus ride today through central london. A boris bus turned
up. Unfortunately as it turned out since the engine didn't turn off once in the
15 mins we were on the bus and apart from a couple of occasions never went
to idle either. Instead it remained at what I'd guess was 1000-1500rpm most of
the way and as luck would have it that was a resonance frequency of a number of
the windows on the top deck. Happy days. Worst bus jouney I've had in a very
long time.

Later on we got on some nondescript hybrid which was a vast improvement. It
was silent pulling away and the engine was only on 50% of the time and when
it was on it was hardly audible when on the move.