The ethernet cable will definitely contribute to having a sound if it’s passing a groundloop and leakage current loop in the system, through it’s shield (not talking about the transformer isolation at each end here, but the shield). It will be system (and hearing) dependent as to whether the effect is big or small or can’t be heard at all, but I do think groundloops and leakage current loops can be a real problem, not something of fiction.
I could be wrong (please do correct me if so) but the Cat 7 spec specifies the shielding to be grounded. If that’s the case I would avoid any Cat 7 cable for audio unless the groundloop/leakage current loop is broken further downstream of course.
As suggested earlier, a great and cheap ethernet cable with a floating shield design is the Blue Jeans Cable Cat 6a (based on the Belden 10GX series). The shield is not connected to the connectors (not grounded) at each end, so groundloops and leakage current loops are broken.
An ethernet cable will also ‘have a sound’ if it’s not even properly constructed to a specification (dropped bits). Blue Jeans Cable also provide a test certificate with each ethernet cable they ship, so you will know that each individual cable is built and tested to the spec.
My recommendation to anyone is stick with Blue Jeans Cable Cat 6 (unshielded) or Cat 6a (floating shield) and be done with it for the reasons above: they’re built and individually tested to a standard and they will break groundloops and leakage current loops. Just my opinion but if an ethernet cable ticks these boxes, then they shouldn’t have a sound (parasitic capacitance is another thing for another day lol).
I don’t think it’s particularly helpful or nice to insult audiophiles in their 60’s or above either. Let’s try not to become the Computer Audiophile forum.