as the title says I have this problem: a loud high-pitched hiss (some 4Khz I believe) coming from speakers when a line input is selected. I have searched for similar problems but all I found seems related to static background noise, which is not the case, or the low-pitched ground loop hum.
I believe it is still related to grounding, but I can't understand how (I have no understanding of electronics beyond the absolute basics).
The hiss is intermittent (going on for bouts of 10-20 seconds each, then nothing for a time between a couple minutes and an hour, then again). It goes up and down with system volume, it is high volume (clearly audible when music is being played), it is irrelevant to music actually being played and it happens consistently on all AC powered audio systems of the house:
- Computer speakers (2.1) connected to onboard audio;
- A turntable's line output, connected to active speakers;
- A turntable's line output, connected to an amplifier's line input and passive stereo speakers;
- A turntable's phono output, connected to a phono stage, then to an amplifier's line input and passive speakers;
- Other kinds of line inputs connected to the amplifier and passive stereo speakers;
- A bass guitar powered amplifier.
It does not happen, ever, when the amplifier is playing other sources (coaxial, optical, digital) or when the computer soundcard is connected to headphones.
The turntable mentioned above is grounded to the phono stage grounding pin, but the hiss goes away only when I personally touch the TT grounding pin. So it can be an issue with the house electric system, but I'm not sure.
Is there anything I can try before calling an electrician? Would filtered outlets, better wiring etc. help?