1.) Does the sound come from the pump? 2.) Is the pump new? 3.) Did you replaice the filter in the resonor? 4.) Did you bleed the sytem? 5.) Option for #2 feed and or return line, clogged squeezing it thrue mainly. 6.) Option for # 3. remove filter see if it increases flow. It deffanantly sounds like a flow issue, if you are sure this moaning is NOT comming from the ABS sytem.