It’s a nylon string – F3. What I meant by xylophonic, it creates a dampened sound, apologies for the confusing terminology. I’m completely sure it’s coming from the grommet because it was very difficult to thread through, from the top or the bottom. I had given up on threading it myself (didn’t want to force it), but a student tried and was able to force it through the grommet.
Thank you for your response.