Been a keen PC silencing enthusiast for many years and I would recommend anyone avoid elastic and, especially, elastic bands!
Elastic will loose its tension after a while and your HDDs will start to sag - and desktop HDDs being at anything other than 90 degrees is a bad thing - while elastic bands will eventually become brittle and snap, mostly due to the heat.
If you use tons of either they will last a lot longer as the weight is spread but I'd recommend anyone looking to do this to do it right go straight for bungee chord.
And no, I don't work for a bungee chord manufacturing company