I just bought a used BMW 318 IS with 118K miles. Everything is working great, even the air conditioner; however when I run the air conditioner, when I park and turn the car off approximately 3-4 minutes after the car is turned off I hear a high pitched (excuse the expression) fart-like noise that lasts for three or four seconds. Does anyone know what this is? I am guessing it has to to with the air conditioner since it only occurs after I run it.

Thank you.

I seem to remember a service bulletin back then that we all laughed at but I don't believe any of us ever worked on or heard a car with the compliant [up here in the NW]. I'll see if I can find it tomorrow. I'm not going to try quote it.........I remember.......it was titled 'Honking and Hooting Noises From A/C'.....what a memory......it had to do with the expansion valve, but I'll find it.

Thanks. Appreciate the help. Do you remember if it was a serious problem?

No, not a serious problem, it was titled "Honking/Hootinh from A/C Expansion Valve" SIB # 64 01 94 (4956). The system works fine with this condition, but on occasion made 'noises'. Replacing the Expansion Valve with updated one equiped with a 'friction damper' cured the problem [apparently], like I said, I never ran across the problem myself but fun non the less...............jeffb.