Clicking clacking tapping rapping from engine bay
 

I have an 87 300D and i noticed it was making a ticking noise after warming up.It seems to have gotten louder and will be faster or slower in conjunction with engine speed.Is thier any check i can do?
i tried to loosen and then tighten the fuel lines before the injectors and the sound did not go away.... is thier an oil or an additive i can use to quiet this thing down before i have to take it apart.it is very loud and i am tired of the stares.thanks

could be the lifters, could be the belt tensioner, could be the chain guides, or bad injectors even. also possible the delivery valve seals are letting in air.
take the belt out, and try starting the car, if the noise is gone, it's either the tensioner or one of the accessories.

ok will try that.I dont have a manual for doing this.do you have to pull on the tensioner pulley to get the belt off?

yes, release the tension.
Could it be a bad vac pump?
Where on the motor is the noise coming from?

if you look at it you should understand how, but basically, you take off the nut from the bolt that passes through the plastic triangle the shock and spring are attached to. put your lug wrench into the hole on top of the triangle, then release pressure so the bolt will slide toward the head. then release the spring pressure, and reach down and wiggle the tensioner and then spin the pulley.
if you feel gritty or side to side play in either, you need to replace them.
both should feel totally smooth and have 0 play side to side.

Also
Take a long screwdriver and touch the end to various (safe not spinning) parts of the engine while it is making the noise and put your ear on the other end. This works like a stethoscope to help determine where the noise is coming from.

It could be a valve lifter or in the worst case a rod that is knocking.
Is the noise a click click sound or a bang bang sound?
How is the oil pressure? At idle and under driving load.
How high is the oil level?
What kind and viscosity is the oil being used?

It could be a valve lifter or in the worst case a rod that is knocking.
Is the noise a click click sound or a bang bang sound?noise is a clicking sound and a rapping tapping sound related to engine speed.it seemed to happed after i put in a fuel treatment additive.


How is the oil pressure? At idle and under driving load.oil pressure is a the 3 bar when cold,2 bar at idle and 3 bar under load.just changed oil a few weeks ago.oil level is between the marker on the dipstick.visosity is 15w-40 mobil delvac