If you want it to play the same sample every time you start the vehicle, you can probably look into one of those old Nickelodeon yakbaks or whatever those things were called.
Basically a mini-recorder that could store a few seconds of audio in a digital format. Rig that up via relay to the ignition, and you might be able to do it.
I'm not sure about getting it to go through your speakers, unless you tapped into the output on the yakbak itself, upped the power and fed it through the AUX input on your HU or something.
Otherwise you're stuck with a fairly low-fidelity mono sound from the yakbak itself.
There might be other mini digital recorders worth looking at that sound better, but I haven't really seen any (or looked, for that matter).
If that's what you're trying to do, good luck with it.
Widge