Well, I have sort of a problem, I have a 2005 G35 coupe with 61,000 kilometres (about 40K miles)

I drive the car daily, including in the winter so it does have some rust (all just minor surface rust as far as I can see) I wash it atleast once a week in the winter and make sure I really rinse the underbody of the car.

Anyways so it just started getting nice out and I've been driving the car like it was meant to be driven (meaning shifting higher then 3K rpms), but nothing crazy and not very often.

A couple days ago I went and started my car and it was suddenly much louder, after a short drive (25 minutes) after I dropped my friend off we both listened to the exhaust and the drivers side of the dual exhaust is MUCH louder then the passenger side. The drivers side is also popping and crackling when the car is revved. The overall tone of the exhaust is quite a bit different now, doesn't sound stock, its much louder and much deeper, I haven't really noticed any rasp, just the popping and what not coming from the drivers side of the exhaust.

Also, the only mod I suppose I have is z-tube intake and a upgraded grounding kit.

The exhaust is completely stock in every way, no modifications have ever been done.

Any ideas of what this could be?

The mufflers are known for cracking at the flange. I would look under there around the inlet pipe and see if you can find soot around the pipe. This will be your indicator of where the crack is. If you can weld just reweld it, if not go to any exhaust shop and they can drop a bead on there for you.

okay, great, i'll look into it. I was thinking about getting some HFC so we will have to see if I should order those first.

Any damage being done by driving the car while this problem exists?

Nah, just making the car sound mean =) I would only be concerned if it is split bad that it will break from the flange totally. It can be welded back together but might cost ya more. Not a huge deal tho!