Rattly tappets on an engine with hydraulic lifters is almost always caused by not keeping to the oil change schedule or using the right oil. Most likely the previous owner(s) didn't keep up with the oil change schedule so the oilways are full of carbon build up...
Sometimes damage to the lifters can be permanent, due to either mechanical wear of the lifters or them being badly clogged with carbon deposits, sometimes its possible to restore them to normal operation by using an engine oil flush or using a specialist hydraulic lifter additive. Just doing a single normal oil change is unlikely to help quiet them down in my experience.
A flush could be done using something like this:
http://www.lubegard.com/~/C-265/LUBEGARD+Engine+Flush
For this type of engine oil flush you first get the engine fully warmed up to normal operating temperature, add the flush, let the engine run for about 10 minutes, then drain the oil and put in new oil. (You probably don't need to change the filter if you've only just changed it) These types of flush try to remove carbon deposits and other contaminants, so this may help.
If that doesn't work you could try a hydraulic lifter additive like this:
http://www.halfords.com/motoring/engine ... fter-350ml
This type of additive you just add to the oil and it is designed to be left in permanently, however I would recommend doing an oil change a few weeks later to get it out of the system. They also take a few days of normal driving before you may notice a difference.
I've used the Wynns additive on some stubborn noisy tappets on my Xantia V6 and whilst it didn't quiet all of them down, it did make most of them quiet. (I think there are still 2 or 3 noisy ones out of 24, but that's better than all 24 being noisy!) It took a few days of normal driving before most of the tappets suddenly went quiet. I changed the oil a couple of months after I used the additive and the ones that were quiet remained quiet.
So the above might be worth doing, however before you do anything make sure you confirm your engine does in fact have hydraulic lifters/tappets - I don't know that engine at all and am just going by what Peter has said, if it turns out it doesn't have hydraulic lifters/tappets none of this will make any difference and you would be looking for a different kind of problem altogether...
