Changed to flats and noticed a slight rattle in my E when played open, that hasn't gone as the strings have aged. I'm thinking the string may be loose in the nut. The rattle doesn't sound as if it's coming from the nut, but from the whole string, but I'm thinking the sound would be carried through the whole string. Fixes? Is a bit of stiff paper in the nut enough? The rattle is very slight.