A silent PC depends on all components taken together as a whole. The thickness of the case does help dampen noise, but if you have noisy components then not matter how thick the case is, you will eventually get some noise.
The primary problem I see the the SilverStone LC02 is the 60mm fans. Small fans generally have to spin faster than larger fans to move the same amount of air. higher RPMs means more noise. The small PSU that comes with it will also have a small 60mm fan which is another source of noise.
Of the three HTPC you have listed, I would have to say the most attractive looking is the Moneaul 972B. However, all three of them use 80mm exhaust fans. Not as bad as 60mm fans, but generally not as good as 120mm fans. You can always search for quieter fans if the ones included are too loud. The LCD screen is nice to look at, but I don't find it to be very functional for my tastes and while it is something I can afford to buy, an HTPC case isn't something I want to flaunt.
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I use the SilverStone Crown CW02 case for my HTPC:
http://www.silverstonetek.com/products/p_contents.php?pno=cw02&area=usa
I bought it for the following reasons:
1. Thick case 0.8mm or 1.0mm of aluminum (can't remember exactly).
2. 120mm exhaust fan. The default fan is pretty quiet, but I'm considering installing a replacement.
3. Able to accommodate a full size ATX motherboard.
4. Has the capacity to install up to 6 hard drives.
5. Optional 92mm fans can be installed underneath each of the two hard drive cages. I purchased two quiet 92mm fans to cool my hard drives (Scythe fans), but it's a trade off. Better to have a little bit of noise than to loose data on 6 hard drives due to heat failure.
6. Tall enough to fit a large HSF on the CPU like the good 'ol Tuniq Tower.
The only bad thing about the CW02 is it is rather compact case for something that can fit a fullsize ATX mobo. If I wanted to install / replace a hard drive, I would need to remove the PSU on side, or the CPU HSF on the other side. Removing the HSF requires the removing the entire mobo from the case. It's not a case for the faint of heart, but I am pretty happy with it.
As stated before, overall noise depends on the components. Other components within my HPTC are as follows:
1. C2D E6600 that is being cooling by my Tuniq Tower. I'm considering disconnecting the fan to passively cool the CPU to reduce noise a little bit.
2. Passively cooled nVidia 9600GT.
3. One WD Black 320GB HDD, one WD Black 500GB HDD, two WD Green 1TB HDDs and two WD Black 1TB Raid Enterprise HDDs.