I went for the free exhaust inspection at kwik fit today and indeed I do have a broken exhaust bracket... no problem, I can get that sorted when my car goes in for it's cambelt change in early October.
Problem is, I'm still not convinced the bracket is causing the rattle. Firstly, I don't understand why I'm not hearing it when idle or in 1st gear, and second, I noticed today that when the rattle occurs I can feel a vibration through the gear stick.
I know I have to get the bracket fixed before I can say it definitely is/isn't the cause, but that won't be for a couple of weeks yet and I can't help but worry in the meantime.
I suppose the real reason I'm so worried is because I work a minimum wage job and a gearbox problem could be a terminal issue for me as I simply dont have the money after spending pretty much all my savings on buying the car just a week ago. I really wanted a special car and I'm concerned I've bought a lemon and wasted all my hard earned cash.
...oh, and before anyone asks, I bought it from a private seller and there was absolutely no sign of the issue when test driving or for the first couple of days... very strange...