[72Nova]

'87 L6 BMW.

anti-lock light is on and mechanical-type noise/rumbling is heard from the ABS box when the car is turned off.

my battery was drained the other day and I couldn't start the car.

my bmw mechanic (he's good) changed the alternator and the car was fine for a week and now the light came back on and so did the noise when the car is turned off.

any ideas?

[Rob (chuck) Berry]

Sounds like the ABS brake modulator valve is geting a "lock up signal" when all wheels are motionless. This could be caused by the electrical relay being burned out and stuck on. If so equipped,remove the relay and replace it with another (like the AC relay) and see what happens. Don't have a lot of specific BMW experience but used to teach ABS in trade school, worth a shot and its free!

[IanRiordan]

Bmw should be like Benz and use an ATE (teves) abs unit. Disconnect the plug from the electro/hydraulic unit and set up a test light, remember Germans use brown for earth (same colour as dirt - German logic) If the power supply remains, start pulling relays, it may be getting power from some other source.
M/Benz units (w202) often throw codes, but seldom drain batteries, could this be coincidence? Another problem perhaps.