My Prime and PSU are silent in standby and when operational. No issues here.

However I do not have SP, it is not a viable option here.

Send it back. No, get the dealer or M to deliver a new one and check that the problem is resolved before they leave with the suspect/faulty unit.

Hector

AV: Thorens TD160B, SME, ShureV15MK2, 500, 598, 861v4, DSP7200.1, DSP3300HC Samsung UE55, SkyHD.
DINING: MS600, AC200, DSP5200SEUG.
STUDY 504, Roon Nucleus + RevB, 808v6, 5200SE, Mac & PC (Touch Screen), Prime+PS Grado GS1000i
HORIZONTAL: M80, MS200, Red Rose Spirit + Sonus Faber Toys, iPad Mini
A capella to Zydeco