Matt Gilbert was tired of using his noisy cassette adapter with his iPod so he added an auxiliary input to his factory radio. Normally this type of thing isn’t possible with factory stereos, but Matt’s 2001 Corolla has the factory CD player as a separate component from the head unit. He starts a CD playing and then uses a toggle switch to swap the sound coming from the iPod with the sound from the CD unit. This would also work with a factory CD changer, but you can’t just plug straight into the head unit because it needs to receive the “everything’s okay” signals from a CD player in order to turn on the input. You might be able to do this with “premium” factory stereos since they usually have a separate amp. All this hack needs now is a clever dock; I bet you won’t even miss that clock.