I've currently got a similar problem on my E12 1977 530i. I've got fairly new strut tower mounts. I think I have diagnosed the problem as a ball joint that connects the tie rod to the center link. When I'm under the car and I twist the tie rod, it binds, creaks, and jerks while it's being rotated. Since they can't be lubricated, at least on my car, it is a good candidate to get dried out and misbehave like this. The creaking noise comes and goes, but seems to be aggravated by heat and by placing a heavier demand on the steering (slow speed, sharp turns).