On the contrary, it's very well known and well understood that EMI / RFI travels ALONG Unshielded / Unscreened cables.
The EMI does not "interfere" with the Ethernet Data within a Cat X cable or with its timing.
Instead this EMI / RFI then makes its way into the Endpoint, thereby negating the work that Meridian has done to make these devices low EMI devices to start with.
This EMI / RFI can then have a deleterious effect on the Audio performance... which is why Meridian are continuously striving to reduce the EMI / RFI present in all their devices to begin with.
Therefore using freely and cheaply available STP Ethernet cabling is something that all users should strive for, especially if their environments are high RFI.
So, are we to assume that your Cat 5e cabling is UTP then from your lack of response to the questions raised?... [and no, Cat 5e is not necessarily Shielded... it comes in UTP and STP variations.]