All of the default vehicles except the Ibishu Covet have the same 'ol boring sounds. For example, the big rig sounds exactly like the Pessima. What is up with this? There should at least be an I4 default sound, V6, V8, and large diesel sounds.
The Covet is a tech demo, to demonstrate the new sound mixing features. In the future, all the other cars will have different sounds as well. Sound is top of the to-do list, infact they're looking to hire (or have already hired) a new sound engineer.
Some of them are from sound library and may be copyrighted while others are noise fests despite them being recorded from actual cars. Alot of people can't make good loops... /= It's a shame really because it isn't that hard to do so. But you'll play with a modded sound and clip clip clip.
Well, they recently put out some job offers for audio engineers, so I'd reckon that new sounds will be coming in early to mid 2016.
I wouldn't hold my breath. All custom sounds will take a while. I would expect it done until version 0.5 or even 0.6.