The first silencing mod I did was to line the inside of the case with the AcoustiPack foam. I like this better than the MagicFleece I used in my old case. The MagicFleece gets messy inside after a while and it sheds fibres. The AcoustiPack is also much less bulky. I bought the kit that is designed for the 3700BQE as it is the same size as the 3000B. All I had to do was cut holes to accommodate the video-card and CPU vents in the side.
The case comes with a plastic fan-mount at the front of the case. The holes in the front of the case are placed to fit this plastic mount, which means that a standard 120mm fan does not fit. I call that just plain stupid! So, I used the method pioneered by SPCR forumite, Bluefront, which uses cable ties to attach the fans to the case and rubber sealing rings to isolate them from the case. This method is very simple and could even be used to fit an 80mm fan to a 120mm fan mount. (read Bluefront's SPCR thread)
To use this method, use two cable ties for each hole. Thread one through the holes in the case and fan, then use another cable tie to tighten it up.
Pictures of attaching front fan with cable ties
This was my final modification. A SPCR forumite by the name of burcakb suspended the entire hard-drive cage of his SLK case using elastic. You can read about his PC, Thor's Hammer, in this SPCR forum thread. As my case has the same hard-drive cage, I thought I'd try the same. I got something called Baby Elastic and used that together with crocodile clips taken from curtain hooks to hold the stretched elastic in place. The drive cage has fittings for four drives so I used the two outer spaces to make it balance when suspended. The elastic is threaded through the mounting holes for drives two and three and up around the optical drives cage. It seems pretty solid and does not move enough to bump the front of the case. I had bought some self-adhesive draught-excluder tape for doors to use as a buffer but did not need to use it in the end. It did, however, prove useful for closing off the metal thingies that block off unused optical drive bays!
At the moment, I'm still experimenting; however, preliminary reports are good. It passed memtest86 and Prime95 with the FSB at 235, multiplier at 10.5, VCore at 1.575v and the memory at 2-2-2-5. With all three Nexus fans at their lowest settings (~600RPM), temps did not rise above 50ºC - seems like I've got a pretty solid, silent-running machine here!