[EastBayE90]

I also have a similar noise but I mostly hear it at idle while sitting in the car when its warming up. It's like you describe a drone type hummm that sounds like a fart and it pulses for a few seconds and goes away. Then a min or so later it comes back. I only notice at warm up idle. I've never heard it after the motor gets really warm. My e90 has 44,000 miles and it has been making this noise since the day I bought it in September with 39,000 miles on it. And it makes it with the procede in or with it out it makes no difference. I just assume its another one of the mysterious N54 noises and I gave up on trying to understand it until I saw this post. Would be interesting to find out what is the cause of the noise.