Sounds like a rod bearing went out as it is a harder knock in one are of the crank rotation. IF it is a rod it would be loudest where it goes from pulling down to pushing up in about a 10 degree arc.
Have you pulled the pan off yet?

Obviously this depends on what engine it is as a W126 V8 engine has to come out to look at any rods other than #1, #2, & #5 as the upper pan that conceals the others will not come off with the engine installed in the car.
jimm1009