I will toss in one more simple thought to check out.

On my 92 SL the split ring on one of the brake pad retainer pins had fatigued and allowed the pin to back out. When that happened, the brake pad slipped towards the center of the wheel and was intermittently scraping on the hub of the rotor.

I was shocked to find that the only noticeable side effect of the out of place brake pad was the noise.

Over time, I noticed that the pins refused to stay put on either side and I replaced them with new ones. The problem did not come back.

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02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)