I am not positive, but I think this "hydraulic interlock" message is only on trucks with lever controls. the fingertip controls give a bit different message. I have not run into one that drained the battery that quickly, but that doesn't mean anything,[I don't work for a Hyster or Yale dealer, we just see lots that are traded in, and I am working from (an old mans) memory,,, not what the codes mean, but the rest of it]. I think I might be inclined to first check the alternator as a point of drain, then the power distribution (relay) box right next to the battery, including all the relays (mainly because swapping it out is fairly easy, if you have another truck to borrow a known good unit from).
Good luck, and be sure to let us know what you find.
It is 'sort of normal' to hear some noise from the throttle body within a few seconds of turning off the key.