Final Tweaks
Obviously, as you use something, you get to find the little faults you didn't pick up earlier on. First of all, it was pretty obvious that the Thermaltake fan was noisy, and blowing against a grille designed to be on the other side of a much larger fan wasn't helping things either.
So I did the first bit of case modification with a pair of tinsnips. I took the grille out. It did help, and reduced turbulance in the airflow, but it was clear that something needed doing with the Thermaltake fan. First I tried making a rubber gasket, which helped, but it was mainly motor noise causing the problem. I decided to hunt for a replacement.
This is what I came up with: a temperature controlled Arctic Cooling 'Arctic Fan 3 TC'. Of all the fans I used in this project, this one impressed me the most. It was the quietest, cheapest, best made and most effective of all the 80mm fans I tried. I cut off the temperature sensor, extended the cabling and popped the little green TTC123 thermistor into the gap between the radiator and the rear fan. Brilliant.
Finally, I realised that the front little Sunon 5-blade fan was making a racket, so this was replaced by a rather pricey SilenX iXtrema 80mm fan. This did the business and really helped pull cool air into the machine in the quietest possible way.
This last photo shows what I think is probably the best watercooling you can get in a MDD case without modifying it in any major way. You could even get away with not removing the grille, which would mean you'd have altered none of the metalwork at all.