Hi to all,
I owned a 1999 ML 320 i was driving it when i heard a beeping sound and the BAS/ESP/Brake light came on.
I pushed the brake which went all the way to the floor.
I stopped and the beeping sound stopped too, and when i took off it came back on.
I stopped again and checked my brake fluid and found out that the reservoir was almost empty. i filled it up and the noise stopped.
The next day it started beeping again and when i checked the brake fluid the tank was empty again.
Before going to a mechanic i want to know what is wrong.
Thanks

It should be obvious to you that there is a major leak somewhere in the hydraulic system. If you continue to to drive it without having it diagnosed you may not stop the vehicle at all.

Crawl under the truck and check behind every tire and check for leaks.