To avoid the interference that comes with FM transmitters, you can opt for an adapter. This isn't possible with every car stereo, but it may work for yours -- whether you have the factory-installed radio or you ditched that for a replacement stereo.
If you have a factory-installed stereo (the one that came built-in when the car was new) with a CD changer, you can use an adapter to integrate your iPod. This involves removing the radio and connecting an adapter to the CD-changer port and then connecting the adapter to the iPod [source: Cabell]. If you have a brand-name radio that replaced the factory radio, there's a special adapter you can buy to integrate your iPod. Depending on the brand, you might not have to remove the stereo to reach the CD-changer port.
A simpler option is using an auxiliary input (AUX-in). Auxiliary inputs are more common on brand-name stereos than factory-installed ones. These connect straight to your iPod through a mini-jack to a mini-jack cable, or a mini-jack to an RCA adapter [source: Cabell]. If the input happens to be on the face of the stereo, you won't even have the hassle of removing it.
Some of these sound transfer options will charge your iPod while it's playing, but not all of them will. You may have to get a secondary power source to keep your iPod juiced.