The guru3d review says
http://www.guru3d.com/articles_pages/radeon_r9_290_review_benchmarks,32.html
In idle you cannot hear the cooling solution and under stress, well you can hear airflow but that's it. The R9 290 will become a bit noisy once it passes a certain RPM threshold, admittedly it takes the R9 290 a longer time to reach that point then the 290X.
http://www.guru3d.com/articles_pages/radeon_r9_290_review_benchmarks,32.html