Could be sticky valves, needs a valve job. Make sure your oil pressure is good and you have your oil full. Make sure you're using high mileage oil. Use Lucas fuel injector cleaner, dirty injectors tend to rattle. Good luck!
It,s lifter noise that your hearing,this is caused when oil doesn't get pumped throught the engine. Iff the oil is dirty and the oil filter is clogged up ,you should change the oil & filter first .You might want to add some (sea-foarm) into the oil to help clean the lifters & engine,it really is good stuff to use,you can get it at your local auto parts store.The engine might run for another ten year with that noise,by the way keep a eye on the oil pressure,you want to make sure the oil pump isn't going out.