Hoping for another set of eyes/opinions.

Went for an airport run yesterday morning and didn't notice anything significant with the car other than I thought it was different that it took a long time for the heat to kick in to defrost windows. I had it on recirc and front windshield for at least 10 minutes at cruising speeds already before I finally felt some heat. Kept eyeing temp gauge and it was steady about 1/2 way. Get to the airport and put it in park and unload the luggage and it started making a constant weird sound with what looked to be steam/smoke coming from hood. Imagine a constant sound from a blow off valve. I shut engine down and get to looking under the hood and didn't see anything. No leaks, and what I though was a puddle from a busted rad hose was actually a puddle of water from a trail coming from the curb. With nothing visible, I start engine and no errors, warnings, codes or sounds. Temp is the same at 1/2 so I drive home in the exact same setup as I had previously and no symptoms. I inspect under hood and under the car and didn't see jack except a small accumulation of some kind of substance on the under body front engine cover. It wasn't oil, or trans fluid...possible brake or power steering I inspect the whole engine bay up top and underneath and didn't see a source of the leaky substance. I ended up just doing a coolant flush including a new thermostat and was not able to reproduce the problem after several test drives.

Sorry for the long winded story, but is there anything like a pressure release valve or what not that would've caused the constant "blow off valve" sound? Again, this happened while in Park and I can't imagine it being a trans issue, but I'm not an Acura expert.

Any help welcomed. Thanks.

 

*update* the hissing sound had returned only once since the original symptom. However, for the last week, I've been having battery drain issues. So far, replace 6 yr old battery and alternator. Thought problem was licked until this morning when it failed to turn over and discovered another dead battery. Before I left to work in my truck, I put a meter in line with the batt and noticed quite a bit of load. Pulled 40A fuse and it dropped some but still something putting load with the ignition off. There was no change with door locks, dome lights etc. Researched a bit and I'm leaning to a faulty AC compressor clutch relay...and like a failed compressor clutch or stator which took out the relay. From what I've read and the symptoms experienced (weird purging sound, weird cold air while heat is on, AC sounds from vents when the car is shut off, 2 dead batteries) it sounds like the relay is intermittently getting stick on and causing the compressor to run. Also look like it draws a fair amount of current even if the car was shut off via the wiring diagram I looked at.
Hope I'm on the right track and I find some damn concrete component failures tonight.

 

Pretty common on this car. That or the HFL unit

 

Got it. Forgot to mention I unplugged the HFL after the first battery just in case, so I've eliminated that. Onto the next common failure.