I work for a small radio station that recently acquired a refurbished Dell PowerEdge 1950 server. After placing it in the server room along with several other servers and sound processing hardware (including a sound mixer), we noticed that the headphones and monitor speakers in our radio studios (which are connected by XLR cable to the mixer in the server room) suddenly started making a low but high-pitched and very noticable sound at all times while the server is powered on.
Immediately, I suspected that some kind of electromagnetic interference generated by the new server was causing this sound, but I don't understand why this server would cause interference while the four other servers in the same room do not. Also, the sound does not seem to get lower in volume when the server is moved further away from the mixer or XLR cables.
Has anyone encountered something similar? Is it electromagnetic interference or some other phenomena? How do I reduce it?