I have had this fixed now, but wondered if others might want to know about the fault.
Within the first week of buying my 2019 sd6 SE the sound system developed an annoying hiss through all of the speakers. It also slightly sounded like a faint noise of a cooling fan. The noise would be permanently there and could only be tolerated if the volume of the radio was turned up enough to drown it out. The only time the noise stopped is when the electrics go to sleep a while after exiting the car. As soon as you opened the door to get in the noise started up again.
Took it back to the dealer and they diagnosed it as one of 2 amps. Apparently there is an expensive one (£1k plus) and a cheaper one (around £800). Obviously, as it was warranty work, it was the cheaper one. I'm sure if it was me paying it would have been the expensive one.
They didn't say exactly what was up, but they fitted a new amp and all is OK now.
It didn't seem like a common fault as they were a bit mystified at first.
