Dude, I seriously wouldn't drive the car till you get that checked out. This reminds me of the Top Gear episode where Jeremy's driving that old Maserati Merak and it was making some serious noise... and eventually the engine got destroyed. If your car is making that sound that loud, I'd be really suspicious and if it suddenly came out of nowhere, I'd be very, very nervous... I'm not saying that it's that serious, it's just really scary. Could be something minor for all we know...
Can't really tell. I can make a few guesses but you really need to have someone look at it. It could be exhaust or intake related. If it is an exhaust leak you shuold be able to feel it (don't burn yourself.) If it is intake related, a smoke check will reveal it. If it is lifters, a mechanic will be able to tell with a stethescope.
