My Birdy has picked up a few creaks after the tour of Kangaroo Island...
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handlebar in stem clamp (likely)
stem in stempost clamp (I see the anodising under the QR has rubbed off a little bit; I think this indicates micro movement)
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Well I put a very thin film of grease between the stem and stempost where the QR clamps, and between the stem faceplates and handlebar, and this cured my creaks.