In my case, cabling was not possible from the main router. So...
(even if cabling is possible, this is an option which can give you same results and you can experiment with diffetent 1 metre cables if you believe that lan cables can affect sound)
a) i bought a wifi extender. tp-link
i connected the lan out via a Ethernet cable to my rpi. 1 metre cable.
It served my purpose. it was good.
i wanted to refine my erhernet signal even further. Since extender contains wifi circuit and it is attached to the mains directly, there would be some electrical noise in the Ethernet signal which i cannot control.
B) Then i bought a passive ethernet / LAN switch. ( again a tp- link) less than rs.500. i connected the lan out of wifi extender to input of switch. then with another cable i connected switch out to in of my rpi.
the tp link switch runs on 5 volts with external adapter and no wifi circuit.
Hence the sound is cleaner now.
i connected the lan out ro my rpi via 1 metre lan cable.
i experimented with another 5 volt supply and the sound was even more cleaner.
Now i can experiment further with different lan cables. i dont need to buy lengthy cables for experimentation. just 1 metre is enough.