I'm supprised that you find it a supprising for a HDD to heat up a case! It's a ~30-40C heat source.
In my situation, before I suspended it the HD was infornt of the intake vent and sat at about 34C with CPU idle temps of around 35.
After moving the drive to the 3.5" bay it wasn't getting cooled by the intake and it's temp was about 42C. The possition of it in the case put it right infront of the HS fan intake so CPU Idle temps went up to about the same as the HDD.
So I suspended a 92mm fan in the spare 3.5" bay bellow the suspended HDD and that knocked it's temps down to about 36C and in turn CPU Idle temps went down to about the same, but still slightly higher than before.
I suppose it depends on your setup what results you get rather than the type of drive, mine was a WD 640GB. Not the hottest HDD I own but still enough of a heat source to effect my system temps when sat infront of the HS.
Silenceing HDD platter noise can only be done with an enclosure, unless you have a highly soundproofed case, or you just stick your drives in a NAS in another room. The latter might actually work out cheaper with the price of some of these enclosures, especially if you need more than one.
I'd like to see you try sleeping in those ear defenders
