You need to toe in the pads, so the front of the pad hits the wheel first.
I've done that for the front pads (5p coin between rear of pad and rim) but not rear brakes, both equally noisy...
5p is probably a bit thick, either do it by eye or a bit of folded card is plenty, riding around a bit getting them to squeal as much as possible can sometimes help too.
@snottyotter started
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I've done that for the front pads (5p coin between rear of pad and rim) but not rear brakes, both equally noisy...