With a whistling sound, I wouldn't look for an exhaust leak, I'd start with areas that can have a whistle sound, like the stock BPV. I have heard that some people leak at around 20 lbs. 19 isn't that far off. Given if all the other hoses and connectors are tight, it's more likely going to be something internal. (I don't think the wastegate would make that sound, but check the AccessPort to see wastegate duty when you're driving. Is the boost dropping when it happens? I've never actually used the "logging" function of the AP, but I'm sure you could do a run (legally, please) to briefly make the car do it, and then stop and check the log. See what the scenario is when you do the pull. If boost drops, you can narrow it to a leak in the "boosted portion" of the manifold/BPV. Are you still on the stock BPV? I guess I could have asked that first.