DAC Noise in DC line

I have installed an Arylic Upstream Pro V3 into an existing somewhat vintage all analogue amplifier. I stream to it using IOS app. When the streaming input is selected its silent and works perfectly, audio is clean and noise free. When I select the phono input on my amp, I get a steady buzz. I measure a 9Hz, 56mV p-p pulse on the 5VDC line. It starts about 10-15 seconds after the Upstream module is powered. Once the module is connected to wifi a high freq “hiss” appears too on top the buzz.

Even if I remove the Upstream module to outside the case and leave only the 5VDC connected the noise /buzz occurs (audio OP disconnected), so it does not seem to be radiated from the module into the Phono preamp. The Phono preamp runs from 12VDC derived from the same rectifier as the 5V.

I have tried a random selection of capacitors and chokes on the 5VDC line without any impact. I have two Upstream modules, they both do the same.

Any suggestions appreciated. If I cannot solve it I will need to power the Upstream off with the Phono selector but that means waiting each time to connect to wifi when moving phone to digital.