I have a Carvin dc727 with fixed bridge. So some days ago I realised that with the low B and E strings there's something wrong with the sound. The strings have a buzzy sound. I realised that both strings carved itselves into the plastic nut a little bit. Any of you guys with the same problem? I checked ebay and there are several choices for a 7string nut. Is there a stiffer kind of nut? I also saw nut made of brass. Can anyone help me to pick the right choice? Because I will order a new nut. I have to add that I don't have that buzzy sound when the guitar is plugged in. But I guess you guys know the problem already. Or is it possible that there is some problem with the frets? I also have to add that the carves that the strings made are not that deep. I also tried to set the neck. but the buzz disappeared only when the low B was uncomfortably high. I'd really appreciate some advices.