I just recently started playing classical guitar. The first time i got it the 6th string always buzzed as i played them, so i asked the company to get me a new set of string as the one that it came with, were old and thought that was the reason. However, after installing the new ones and tried to cut off any excessive string that might produce it, buzzing still occurs. Is this normal for nylon strings that haven't yet settle in? Artist HG39303 is the guitar if that helps.
When you hear the buzzing, try touching small bit of string between the bridge and the peg. If this is the case, you can install a dampener (bit of rag) or restring that string (do an image search to find different ways of tying a classical string).
Another possibility is the string between the nut and tuning pegs, but that shouldn't be as loud.
Last, it could be wiring from electronics vibrating inside the soundhole (but again this is very quiet compared to the first possibility).