Does my Turbo System Have a Leak?

Hey everyone, to give a little background I'm pretty new to the general mechanics of a car, I understand everything to a basic level on the main components of the engine block and items connecting to it, but can't just look at an engine bay and tell you what every single piece does.

Recently my STI started to drop boost, where as it was originally able to boost easily up to 20+ PSI, it dropped to 17, and now 15 or maybe even lower (I haven't reset my boost gauge's memory, but I only see it spooling to ~13-14 currently). Yesterday, my friend asked if we could install a turbo blockoff valve because he wanted to hear turbo flutter when we rode, I agreed saying I'd do it under the thought that I could get some videos, drive around for the day then take it off. But when we installed the homemade blockoff, nothing happened, I thought it could have been the shotty craftsmanship of the blockoff not getting a good seal, so I cut another aluminum piece from a can, put a hole in it so a screw on the turbo bypass valve could hold it, and put it on. Again nothing, not even hints of flutters, nothing. I thought alright, maybe I positioned it wrong, so I took the TBV off again, repositioned it and cranked it down. Drove around, again nothing. Finally I was fed up thinking that it was just not getting a good seal, I went to Home Depot, got a piece of sheet metal steel, cut an exact copy of the gasket without the port hole in the middle, mounted it, cranked it down, and again nothing. I was defeated in my quest for cool turbo noises, but still confused. I thought about it and I wasn't sure what I did wrong.

Can anyone shed any light? Could the hose from my turbo to the intercooler or my intercooler itself be leaking air? Or what am I doing wrong when installing the BOV besides DIYing it? And if it is just an issue with my BOV, why is my turbo dropping? The car is new with only a couple thousand miles on it, so I don't think it's premature wear on the turbo?

Thank you in advance for any help!
-Rocky

If your car is stock you weren't seeing 20+ psi. STI's max out at 17 PSI and its not even efficient at that PSI.

Next, stop letting your friend talk you into doing stupid things. Turbo flutter is not a good thing. "Blocking off" the turbo is a good way to blow it up due to compressor surge.

The only way to find out if you have any leaks is to do a boost leak test.

Reading into turbo flutters, I've heard many calling it "the easiest way to blow up your turbo" and other stating "it's not harmful as the air flows back after the turbo has already stopped spooling", I get the risks and I appreciate the concern. About the possible leak though I'm assuming it's probably not worth it to buy a test kit for a drop of <2PSI until further drops happen or boost just stops all together?

Did you check the clamps on the tubes?