Howling noise from Clio steering rack

hi,

I have a 2004 Clio Dynamique 1.5 diesel.

When it is warmed up, after 5-6 miles, there is an intermittent howling noise which seems to be coming from the steering column and gets louder, then it stops, then starts again. The steering wheel vibrates slightly when it is making this noise.

Any ideas what may be causing it?

Thanks!