Asking for a friend, of course. *shifty eyes*
Try just hot water first, if this does not work add a little dish soap. Make sure to use the plain hot water after, you do not want a slick surface to run on. Do not over do it with the soap, it may dry out the belt causing it to start to get cracks in it. If you know how to remove the belt take it to the car wash to do this.
as the neighbour of someone with the loud horn sound i understand. locate the wire coming from the alarm system to the horn. disconnect it and hook it to the sound generator of your choice.
