Often only one in use though
The HST is designed to be at its optimum with both power cars, and if it is running on only one engine then the train soon looses time. Of course, I haven't really seen them since they changed the engines to MTUs, but certainly that has only been the status quo for the last 30 years!
I also need to point out that the MTU is considerably quieter than the old Valenta engines which had that distinctive screaming whine noise. I am presuming here, but you might simply not have heard the MTU.
We once went "Cross County" from York, and then tried to get off and change trains to find the platform side door would not open. The next platform on the other side was not until we returned to York so we had to go via London. Guard tried to make us pay a London supplement, until we pointed out that it was not by choice.
Eventually after some 30 minutes trying to sort the door, we ended up exiting through the cab!
What door, on the Coach, the guards van on the HST or a DVT?