MBDriver

I was driving today at about 2 pm and the weather was really hot in my area (98). I had just driven home from my cousin's house. I had the AC on when I was driving in the city near his house and in the freeway coming back and to my house after I exited. The temperature gauge was reading just about 100C. I came to a red light and when I took off, I heard this weird ticking noise from the engine. It only happens when I press the gas. Does anyone know what this might be? I have an 01 E 320. I tried to hear it with the window open but I can only hear it with the windows up.