Correctly identified prob with the APU bleed valve.
The "Barking Dog " noises come from the hydraulic PTU (power transfer unit) . Yellow system (Using a elec pump) is also powering the green system thru the PTU . Basically it is a back to back motor/pump assembly. As soon as L/h engine spools up the EDP (engine driven pump ) will take over and pressurize the green sys and the PTU will stop.
