190E Noise/judder on full steering lock

Another slight puzzler to me, as my '87 190E is my first car to be fitted with PAS, is that on full lock, I get a judder/vibration feeling at the steering wheel, and a sometimes quite loud noise which is hard to describe - but the car's clearly letting me know it doesn't like it! My Haynes manual says full lock strains the PAS system, but doesn't mention this noise or shudders - is it normal or do I need to get worried about it (car's been like it since I bought it over a year ago)

Appreciate your help!