87 nissan metallic rattle during operation

my engine is a 1.6 tbi and it is excessivly noisy and has a metallic noise during operation. My timing is correct and the oil is up. could it be valves or what?:eek7:

I adjusted the valves and installed a new timing belt. All okay. Thanks for all the help...not.

glad u posted this...i have the same problem with my car..got it fixed though...thanks for all the help i here...yeah right!