So, some interesting things about the ARB compressor.
I pulled it out and pulled the tank off. I couldn't see any debris in the tank valve or the reed valve on the top of the piston.
I put it back together and hooked it up, then ran it with the engine off. It ran like normal, pumped up the tank in about 15sec.
I bolted it back in (PITA cause of where I mounted it) and again ran it with the engine off. ran like normal still.
Start the engine and with the increased voltage from the charging system, the compressor spins a lot faster. With engine running, I had the same problem of the pump continually running with varying sound, like the reed valve on the piston isn't closing.
I called ARB USA this morning and they asked me to bring it in so they could bench test it. They are only 10 miles from me but it's 10 in the opposite direction of work.
I'll drop it off tomorrow and hope they can figure it out ASAP or give me a new one.