Noises problem
2006 BMW 525 6 cyl Automatic 70,000 miles

I just recently purchased this car used. I noticed a few days ago a noise coming from turning the steering wheel. The noise level also seems to get louder upon acceleration. When I'm coming to a stop I hear the noise when turning the steering wheel. I have checked the computer diagnostic systems and they all check ok.

How was the test performed?

The car has the i-drive computer that will check automatically different things like the oil level, brake fluid level, brake pads, etc. However, I cannot find where it checks the power steering fluid level. I read through the manual and there was nothing in there about checking the power steering fluid. I also looked under the hood last night and cannot find where you check it. I'm not sure that the power steering has anyting to do with the noise but it's the only thing I could think of. The noise is like a humming or buzzing sound and it doesn't always do it- only sometimes. I thought about taking it to the BMW place and asking them.