noisy v brakes

i have just finished putting my hardtail v brake build together and my xtr brakes are making the the most horrendous squeal when the brakes are applied, i have even tried warming the pads and rims up whilst riding put this doesnt solve the problem? there doesnt seam to be any pad rubbing the rim when freewheeling so i am assuming they are aligned straight enough, its the 1st time i have used v brakes since discs where introduced, help my ears are starting to bleed
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spaced the back edges out.
see park tools.
Parktools :?:SheldonBrown