It was another milestone in the demolition of the Metrodome on Sunday when the cables that supported the facility’s roof were severed as construction crews set off about a dozen explosive charges. Mortenson Construction said before the blasts that the noise would have a lower decibel level than the pyrotechnics used after a Vikings touchdown. But the noise still prompted about a half-dozen calls to police. The Metrodome is being torn down to make way for a new billion-dollar Vikings stadium. Steel installation for the new stadium is expected to begin in August.