i had the exact same problem when i use to use 91 octane fuel on me ek, and noticed the sound went away when i used 95 or 98, but if i used 91 again it came back.
I know it sounds a bit far fetched but it works for me, this is the reason i use 95 octane in my ek : / .
let ur tank drain and fill with 95 and see if sound goes away.
I can nearly guarantee it will
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