Sometimes I get a knocking or tapping sound coming from the ABS block. It's a 104.995 engine, 1998 E 320 4 matic wagon. Brakes work fine, fluid level is correct and doesn't look discolored, but not sure when fluid was changed last. Anyone run into this before? Have an explanation or a fix?

Are you sure that the noise is coming from the ABS unit? There's a small piece with a "MOT" label nearby which is somewhat noisy (or so I am told; I have an oiler).

Pretty sure it's from the ABS block. What is the MOT? I'm not familiar with that or the oiler you mentioned?