a HONK sound? lol now im really curious, can you post a little video of of it?
anyway, if you are under the extended warranty, i definitly recommend sticking to mods that can easily be unbolted back to stock.
Additionally, find out from your dealer (or any other close by ones) what kind of mods, if any, they will allow you to do without voiding the warranty.
that way you know which mods you would have to unbolt and which you can leave on any time you have to take your car to them.