Rattle on start up

Hi,



I just bought this car, used, 10th June.



What has recently started to happen is some sort of rattle noise on engine start up. This noise does not happen all the time but irregularly. I've tried to record it but just waiting for it to happen again. However, I found a link on YouTube that sounds exactly like the noise.







Note; my engine does not cut off after the noise, it starts while the rattling continues for a couple of seconds.



So, I guess what I'm asking for is some advice on what the problem may be and such



Thanks