The HD cages on my Chieftech case rattle, actually it's the locking handles that rattle occasionaly. If your Lian Li 50 is built anything like my 60 then I'm sure the rattles either the HD cage or one of the chassis pieces that's fitted with a rivet that's not holding the panel tight.
To find out where it's coming from start putting your hand on all the different parts of the chassis until you find the place where touching ti makes it quit.
Iknow of the rattle you're talking about since my upper HD cages locking handle, when tight, would actually not ahve any tension on it and make a metallic rattling sound. It's a light sound but very annoying. Not a consistant sound you can get used to like the whir of a pump.
Aluminum cases aren't very good for making quiet cases out of. AL isn't very good at dampening and with aluminum being so light it takes very little energy to make it vibrate. Any loose rivet or mechanical device will cause a rattle. So even 5 inches of padding on the mounts will still transfer enough motion to make buzzes.
If you want to make it as quiet as possible you can make the panels dead quiet.
It requires taking the case apart though. You could take the case apart, in other words remove all the rivets, and where every panel or brace meets another place some 1/4" self adhesive weather stripping like you find in any hardware store. Then get some Dynamat or any other self adhesive sound deadening material and place pieces about 3/4's the size of you side panels to each one. That saves on the amoount you need and still does the job.
You caould also place weather stripping pieces in small strips on the HD cage or any other removable part so that when they touch they are resting against the WS and not AL to AL.
Anyway, thought I'd throw those out there in case you found something useful
