I recently bought a second-hand Audi A4 SE (2003).  The steering was
fine at first, but now (after doing around 3000 miles) it is rather
heavy and the resistance of the steering wheel is inconsistent,
especially at low speeds.  This has made maneouvering the car around
roundabouts and town streets very uncomfortable.

Another thing that I have noticed is that the steering wheel does not
sit dead-centre when I want to go in a straight line.  I'm pretty sure
that it did when I first got the car.

Does anyone have any ideas what is going on and what the best thing
would be to fix this?  Has anyone experienced similar problems?

Thanks in advance,

Andrew