Power steering fluid level

On the upper section off the steering oil contender you have a rim ,the oil level need to rich this one,all the best.

Have you checked relays and the fuses

hose or connection most likely has broken, have you lost fluid aswell? take it back to the garage who did it they might sort it out for free as long as it's not a burst hose

Also note, in these cars they use AUTOMATIC TRANSMISSION FLUID for their power steering system, so don't be alarmed at the colour.

Check the steering rack to make it's not leaking, also verify the fluid level in the pump.

Check the trans cool hoses from the trans to the radiator.
Try and find where the fluid is leaking from.
Let me know what you find.

It might be a faulty power steering pump. Try checking the level of the power steering fluid. It is probably best you have your power steering system checked by a mechanic.

Does the noise occur only when the vehicle is moving?

Try moving the steering wheel from side to side, while stationary (but don't do it too often, or you might damage something). If the noise is still present when the car is stationary, then it probably is the power steering system.

If the noise only occurs while the vehicle is moving, it could be a problem with the differential/final drive, or even wheel bearings.

when looking at the engine with the hood up, look to the right hand side for something that looks like this (#1 in the pic): http://www.realoem.com/bmw/showparts.do?model=ET37&mospid=47720&btnr=32_0957&hg=32&fg=20

it will be black in color, but don't confuse it with the oil filter housing. power steering reservoir will have a unique cap (#2 in the pic) that can be removed with your hand. the one that has the large nut on top is the oil filter. remove the cap and put in the correct fluid.

hope this helped.

Make sure you check your power steering fluid... if it's even low, it will make a terrible noise...run it on empty too long and your can ruin your power steering pump.

if the power steering fluid is full and belts ok but, it happened suddenly, provably the power steering pump shaft was broken.