Yeah, I know there's no problem with arctic silver as far as it working - - but since I always get the retail box chip (you get your warranty for only $10 more usually) I have to worry about voiding it.
And you're correct in that a cheap case will be (usually) noisier than a more expensive case, but I'd rather put the money into making the computer more powerful. One thing I did with one of my cases is to line the sidewalls with Dynamat. Quieted that sucker down like you wouldn't believe
