There's nothing out of place when Q gets home--either physically or with his wards--except the item in the living room.
Sorry this is late, but after you said he didn't want an electric keyboard, it took Sev a while to think of something else. A piano is a little beyond him, and sneaking one in would have made him feel like Slughorn... Er, you can pretend the decals away, if you want. They're a pure coincidence; this was the only dark-wood dulcimer I saw. But it is quite a coincidence, isn't it? :D