2001 ML 320 driven home last night and ABS light came on, followed by a loud air hissing noise under the hood somewhere by the left strut tower. Not by the firewall or the front of the car, this sound is coming somewhere around some components in the vicinity of strut tower and engine. Turned off the engine and removed the key but the sound continues. check A/C lines everything ok. Coolant system is fine. Removed the postive battery terminal and the noise stopped! Put it back on and it continued, so I left the terminal off. It doesn't sound like a motor turning, it sounds like alot of air. Would vacuum continue after engine is off and key removed? can someone give me some insight to what this could be?

Sounds like your hearing the fan in rear of main fuse box to cool the modules they are known for noise. Pull cover off fuse box and listen after you turn key on! Was it hot yesterday maybe modules are overheating in traffic. Tim

I heard something similar the other day when I got out of my car (02 ML320), it sounded like a water sprinkler or a major hole in my tire. It continued for like 15 minutes. My husband got under the car and he said it sounded like it was coming from somewhere along the exhaust. Odd thing is I have not heard it again... I however did not have the ABS light- just the usual check engine light.

Yes, it was very hot yesterday, A/C running good, stop and go traffic. However, I left the positive cable disconnected overnight. The next day, reconnected cable, and haven't heard any hiss/air. If this happens again, I'll check fan for fuse/relay box and reply. Thanks.
Oh, by the way, Princess ML, your right on target, it sounded just like a major hole in the tire!