I just remembered something I saw once. I saw a harpist on a tour practicing in a house where she was staying with some people who were hosting them. So that she didn’t bother them she put a scarf (thin) through the harp strings. She said she doesn’t usually do that because she likes to really listen to her tone every time she plays and she can’t do that with the scarf (obviously) but that in a situation where it’s really important to practice without bothering people she does this because it muffles the strings. I think she had to practice at night while they were sleeping because she was doing so many events during that week in the daytime and early evening. It’s really important though that the scarf was really guazy and thin like one of those 1950’s sheer scarves. So it didn’t bend the strings at all but it really made the harp soft.