Room we were given was next to one of the internal generators. We asked about the noise but it was a known issue, rooms 130,230,330,430 are all next to the generators
Same goes for rooms 205,305,405
After being told no alternative was available, and trying to check out at almost midnight, a new room was magically available that had no humming duct noise, but the fact it took the effort of packing bags and getting a taxi elsewhere wasn’t good enough from the hotel service point of view.
Malmaison used to be ok, it’s premium economy at best these days. Staying at Premier Inn would have probably been better.