hi, i bought my polo yesterday but on the way home the engine started to rattle at idle. like a cylinder was out. so when i got home i did an oil change, new plugs leads, distro cap rotor arm and coil pack. the rattling has more or less gone but the engine is now making a tappety noise, so i have checked the compression on the cylinders and it all seems good, i have no idea what to do next, im quite good usually being an almost qualified engineer (student)

any help would be greatly appreciated.