Goldtec cassette rattles about a bit. Need a super thin (1mm I reckon) spacer to pop at the end of the cassette to let the thingie bind down and make it tight.
I have a couple which I could send you, but to tell the truth I have always ran a homemade gear set up/cassette of 1x5 - and when I need one of these spacers I just go to any bike shop with a mechanic and ask for one, they usually have a box or two of spacers hanging around and often will give you one or two for free.