What does a stock Titan fan sound like at 100%?
4 overclocked Titans @100% don't even get close to a single R9 290X @100%
Having said that I don't think the 290X is that noisy in normal use. If you are going to overclock the nuts off of them you are going to fit a waterblock anyway.
To put things in prospective my Asus Matrix Platinum 7970s when running with their fans @100% make quite a noise, right up there with the 290X but I don't see a lot of negative comments about the Matrix Platinums.