I found a Specialized bulletin saying that one of there bikes fitted with Avid Something-higher-in-the-range-than-7s needed to have the rotors changed to solid ones due to noise issues. They were changing them for free.
I have just bought one second hand so will report back when it turns up and I’ve had it on a while.
My 7s squeel like hell and I can usually fix them temperarily by cleaning the pads(sintered) off on wet’n’dry and applying copper grease to their backs.
I reckon it is something to do with the damp getting into the pad matl at this time of the year and then not getting warm enough to dry out and keep the contact surface of the pad in the correct condition.
Just a guess though.