This happened to my W123.
Front right bearing was to blame.
I jacked up the car and moved the front wheels to and fro.
The front right had movement while the left was tight.
Changed out both bearings and noise gone!!!

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1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
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1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD