I can't find an overpressure warning in the QRH, so I think the valves just blow and then you deal with the resulting "cabin pressure" message. It does mean you are reliant on the overpressure valves working though - perhaps that is why there are two?
The 767 has a "whoosh" noise when you retard the thrust levers at TOD as the packs go into high flow - it was a similar noise I heard in the cruise yesterday that made me look.
Bullethead - I love 'em both, but the 767 has the edge I think. Better control response in roll and its just got a bit more space and stability and flexibility. Having said that, I love a light 757, pointing it at the sky and just climbing away. Then again doing improved climb in a 767 at max weight and rotating at 175 knots is good fun too! They are both very capable aircraft but the 767 just feels better. The 75 is a bit more agricultural if that's not too harsh a word to use, and the 767 seems to smell less - horrid toilets and oily aircon in the 75.