Re: Anyone ground the HU twice?
Some of the factory harnesses just wire into a common ground. This is the type that would give you noise, or sometimes clicking when various devices kick on.
If you have noise, then I would switch your ground from the harness ground to a dedicated ground to bare steel behind the dash.
'65 VW Bus
MA Hippo 122, (2) Aura Sound 8's, (2) SoundStream 6.5 coax, (2) Alpine Type-S 6x9's [rear fill], MBQ DSC1500.1D, RF 501X
'02 BMW 330xi (AWD coupe), every option
Harman/Kardon 12-speaker System Option + Dayton HO D4 10" and PPI Ion 650.1 in sealed box
And many more car audio goodies in storage