Two problems.
Premier Room in the Annexe. First key didn't work; twice back to reception 100 m away so had to go back and forth.
Room spacious, BUT, a dreadful hum like a pump quietly, getting louder, cutting in and out every 2 mins, so impossible to sleep with this constant reverberation going round the room. A motor is either next door behind the wall or above in the cavity. Unacceptable to rent out to customers. Hotel should have been aware of this big problem. Had no idea. I spoke with the receptionist at the desk who was reluctant to get the manager. Why should one be charged for this lack of premier treatment? So be wary about staying in the Mercure Premier Rooms. A dissatisfied customer.