An old Quad 34 preamp was picking up computer noises and hiss etc when connected up to a Raspberry Pi based audio streamer.
The preamp had bad earthing (so bad it would have failed a PAT test), burnt out tracks on the PCB and a snubber network across the input to the mains transformer that had self destructed.
After the above was repaired the unit worked properly.
The Quad 34 is an interesting design as its got a lot of logic chips in it which would make fault finding less than straight forward if it had a major fault!
Please contact me for a quote if you need some electronics or hifi repaired.