vibrations from front middle of car

Hi All,

I hope someone will be able to point me in the right direction. My audi a4 has recently developed a strange vibration, particularly noticeable at low speed and it starts after about 15 minutes of driving.

It seems to be coming from in front of me towards the centre of the engine. If i go over a bump, it will make a strange sound like something is moving around. I am fairly certain it is related to my steering rack but I could be mistaken. The reason I suspect the steering is that when i sway the steering from side to side, it does give me a similar knock sound.

Any ideas and suggestions will be most warmly welcomed.

Thanks for the response Gordy. I am taking it in to the mechanic in a little bit, hopefully it is nothing too major. I will update here later with results in case anyone else every suffers this problem.