Alternator not charging at idle

Hey...
As the title says brand new alternator is not charging at idle. I get a reading around 11.5v at idle and will climb to 14.4v by 1500rpm. Before I pull it and bring it to be bench tested, is there anything else to check? Would a grounding issue cause this? Belt is tight. Alternator is the 140amp model from BP Utah.

One other note with the ignition on & engine off the speakers have a very noticeable whine. Seems to go away with engine running or at leasts gets drowned out.

Thanks!

Another observation while testing. With ignition on engine off, the alternator hums and goes away when charge light wire is unplugged.