Hi all. My X's horn is working not well. When I push my horn for a while, say several seconds, it sounds weird. The horn sounds unstable, sometime in normal tone, sometime in lower tone. I guess maybe the higher tone horn does not work well. Anyone has any idea? If I need to replace my horn, just want to know where the horn locates under the hood and if it is easy to replace it. Thanks!

__________________
--2004 E53 X5 4.8is - ECE version; right hand drive; Located in Hong Kong; ext. black sapphire metallic; int. leather black; adaptive dynamic bi-xenon headlights; 16:9 onboard monitor w/o navigation; 20" genuine BMW Y-spoke 214 wheels with Bridgestone Dueler H/P Sport tires; Int. rear view mirror w/ compass.