my timming chain is loose and hitting on my car and making noise

seek a 2nd opinion from a good mech not a chain store. how many miles on car?

If it sounds like 'marbles banging aroung in a can', there is a good chance the chain is okay. Nissan timing chains are set to proper tension by oil pressure tensioners. Check your oil level it is probably pretty low. If it is low, fill to proper level and the noise will very quickly go away as the tensioners get more pressure to exert.