Ever since buying my C240 it has had this tick noise that is sometimes very loud, sometimes there is none and sometimes it ticks with the revs until 2500-3000rpm then goes away. I noticed as i shut of the car with window open that my exhaust sounds little deeper, So i started it up again and it sounded little deep and no tick then i reved and ticking came and exhaust sounded normal. I went out for a spin and it worked awesome very quick and pulled harder than normal. But sometimes i feel like it lags power like going from 70 km/h to 130 km/h feels like E230 w210 with full junk in trunk. But sometimes it goes flying no problem.

I’ve trying to narrow my problem down i think maybe Catalyc converter the front? Because the ticking seem louder underneath the car.

I had similar noise in my old E430 but that was just normal m113 tick noise that they all have or 98% from top of the engine.