i have the same problem. drive me mad.
anyway the garages i went to, all told me different things, including nissan.
Personally i dont think its the motor, on yours but the bushes. Spray some wd40 on all the joints etc and a good remover or screen wash on the windscreen, this may help. although i have already done this, it helpped but still the problem exists.
the best thing u can probable do is replace most of it, get it from the scrappy. i should be doing mine this week, so will let u know if its not that.