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I'd be checking wheel bearings or maybe CV joints mate.

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ah both, personally, i'd go see a mechanic/wheel spec. where abouts are you located mate?

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My car does a similiar thing, when I have the front windows down i can hear it, and yes the slower i go the less frequent you hear it. It's like the brake pads are touching the rotor ever so slightly that it makes a tiny grazing sound each time it spins around. Can really notice it at 60km too when driving along next to a concrete barrier. No problems though, but the brakes are squeaky, don't know if that has anything to do with it. It also did before i got my current set of wheels, so it must be the brake pads or something for mine then?

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Sounds like it's your wheel covers walking or moving on the rim causing the squeak....if no squeak with them removed then it's definitely the problem....maybe spray with silicone spray or bend the clips.

Wheel covers definitely make an odd noise when they're not on right, I've fixed one or two for people while out and about (they drive by in car park, if they park close, i tell them and fix)