I was worried at first that it might be the turbo (!), but no- it's definately the exhaust. The thought of a loose catalyst core also came to mind and it may be that when very hot, the expansion in the metal is just enough to make it loose. Also, the idling revs are a tad lower when hot and this helps excite the resonance. I don't think that it is anything serious, though, but I'll keep an eye (ear) on it. As I said it's only when it's been driven hard and then it goes back to normal after 10 minutes. Maybe it's normal and that's why I placed this post to see if anyone else has experienced it.
Otherwise, the One-D is really great and loads of fun. |