Clanking noise, only under load
 

My car seems to have started making a clanking noise but only when under load, and it doesnt have any kind of consistency to it. Not like a ticking of a valve, but it sounds to be coming from the valve cover. When the car is in park and I rev the engine this clanking is not audible, but when I put it in drive and give it gas you can hear it.

Anyone ever have this before? I figured I would pull the valve cover this weekend and take a look, but i dont really know what to look for. The car idles fine, no stalling or any real roughness to the idle.

91 190e 2.3

After pulling valve cover, I see nothing wrong. I pulled the coil plug and had someone crank the engine while I watched but there is nothing I can see.

Is this noise one that can be caused by the belt tensioner shock?