Thank you so much for this response (as I know the post is really old)
I have an e53 x5 2005.

So if I understand your post properly, the fan running in the IHKA unit after turning the car off is normal? I did happen to be sitting in the car for about 20 minutes and I did hear the car completely shut off after 16 minutes and the fan stopped.

Does this mean that I do NOT need to replace the IHKA unit? That's what I was told because the mechanic never heard of the unit making that sound for so long and he suggested that perhaps that is what killed my battery.

Thanks!

-PRDivaMichelle