When shut off the car, the volume is at a certain numerical level, and when I turn the car on again, the volume is still at the same level numerically, but its MUCH louder.
It's more than likely because you're used to hearing it when you shut the car off, then it's kind of a shock to your ears when you get back in later and turn it back on. Normally I'll turn the volume down a bit beefore I get out.