Another vote for wheel bearings. My bearings did what you described consistently, regardless of conditions, turning, etc. You should have seen those things when they came out. I couldn't believe how quiet it was following replacement.

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Chris

'04 ML500 - 53k, Inspiration Edition, Desert Silver
'11 Audi A4 Avant - Brilliant Black
'87 300SDL sold
'99 C280 Sport sold
'85 190E 2.3 sold