there are 18 of them, one on each rocker arm as seen in the below picture :

 

Ok, given the climate down there, I'd not run 0W40, I'd run either 5W40 (what Mercedes is telling dealers to use) or 5W50 (what I use - both are on 229.3). The heat of North Georgia leads me to use 5W50, maybe a bit extreme, but that's me. It is certainly warmer where you are.

The lifters are hydraulic and use oil as their medium. If you increase the weight of the oil, the lifter(s) may be happier.

Of course, maybe it's not a lifter, I DO KNOW that our injectors are kinda noisy in these engines. But it sounds like you have one (of which ever it might be) that is way noisier than the others.

Hard to say from here.

Here is hte current approved oil list:
MB 229.3 - Multigrade engine oils (Specification 229.3) - Mercedes-Benz Specifications for Operating Fluids

 

Remember, FLEECE filters ONLY, no paper - here are too good choices:

 

FLeece on the left, paper on the right:

 

I've been definitely been using the puralator brand filter no doubt. I am gonna have a Mercedes mechanic look at my vehicle. I just want the noise gone and my car to be ok. I've invested a lot in my car and I'm trying to take good care of it.

 

Damn it I just realize the paper one is what I've been using but in the puralator brand. Ok so for my next oil change I'll definitely switch it. Honestly Ive just been following the engine label, it's says to use 0W-40 so I really wasn't aware that I could switch it due to the heat/climate here. Learn something new all the time

 

The tick could be lots of things. Perhaps as simple as carbon build up in one of the cylinders. Find the place the noise is originating from and the possible causes become fewer.

Les

 

The highest tapping sound is the same as mine and as soon as you touch the accelerator it stops, I've had someone have a look and he seems to think it is the water pump, I am not a mechanic by any means 2 other people think it is the Aircon unit as that has stopped working, taking it to the garage tomorrow so hopefully will get some answers but these cars are a one of a kind when they start acting up, the engine is smoother than anything else I have owned so far so my head is hurting over that tapping

 

Just remember, mechanically, it is a 2003 Mercedes SLK320. Be sure you take it to someone that knows Mercedes.

 

I am not a mechanic but the knocking sound appears to be coming from the front of the engine and might be cam drive related. The timing chain and/or gear could be worn to the point where there is sufficient backlash. Large amounts of backlash will cause a knocking sound at idle rotational speeds which sometimes sounds similar to a worn connecting rod wrist pin. Once the engine speed is increased the sound disappears. Maybe someone on this forum has a method for checking this possibility.