Horn is fixed on my 02.5 P5.....
 

My horn started to get "weak" sounding to the point of, pressing the horn it would only buzz from under hood (Not good on the streets of Boston :D )....no power loss or loose wire...actual failure of the horn itself..dealer had to get it shipped since this was a fluke...and I bet they don't replace them that often...I was in and out of dealer in about an hour....
Almost 6k and still really liken the car...carry on folks !

i still LOVE my 5... nearly 2yrs later :)

have you tried pressing the horn down for more then say 30-45 seconds? the tone changes after that.... like be becomes distorted..... kinda like dying sound..... fromm a high beep to a low beep....

thats kinda how I noticed....I thought for awhile it was a power issue....(BUT didn't see lights dimming etc).....it got progressively worse to the point all I got was a buzzing sound from underhood when horn was pressed.....They actually replaced the actual horn (diaphram?) itself......If u have same issue get it checked as it is dangerous with no horn....gotta keep the car pretty :D ...and for public safety.......

i was thinkin about changing mine out. it really sounds bad, cheap etc.. anyone done an air horn or any other horn swap? thanks, joe.

Air Horn by Hella
 

I have install a set of Hella air horns (two trumpets) in my MP5, they had to take the grille out and build a braket in order to meke it fit nice.
I tell you they sound sweet, I make people jump out there seats
with this horn, I paid like $35.00 to $40.00 usd + installation $20.00 you can't even see them at all.
I will recomend It to anybody It sounds like Ferrari horns.

I have a high note and low not fiamm horns in my car. They sound like an expeditions horn...pretty sweet and loud!!!

That happens because the horn heats up. Horns draw a lot of current and make quite a bit of heat after prolonged usage. Standing on the horn for long periods could eventually damage it.

there was a somewhat recent extensive thread about horn upgrades....I may upgrade at some point