A brief explanation to start things off: A have a custom made h-pipe and when the muffler shop was cutting and welding the pipes it let off a strong smell, that of burning metal. The pipes seem to be made of stainless steel, if it matters. At the moment it seemed like a normal thing, afterall, pipes were being burnt and melted. When they finished, I went home and as soon as I got out of the car that strong scent was there. I dismissed it as being normal. This continued for the next 3 weeks until I went back because the driver side was making some rattling noises. I told the guy about the smell and he stated it was normal and that I just need to give it some time til it burns away. A few days later, most of the smell went away so I thought in a few more days the smell would be completely gone. Its been about 5 months now since I got the dual exhaust and the smell is still there, but only after I floor it for a good moment or when I drive in excess speed. The smell goes away in about a minute, but you can smell it emanating from the car as soon as you get out. And if I'm driving with the AC or the defroster on, the smell starts to fill the cabin. It isn't a major problem to me, but its kinda annoying to have to deal with that. What can be causing this problem? A slight leak maybe right after the cats? Or just cheap quality pipes?