I would start by going back and rechecking all connections dealing w/the install.
Anything that was loosened or disassembled for the installation would be where I would start to look.
Lol hook up a vacuum? Why go through all that when you already said you just had a new dp installed and two separate people told you to check the connections? Just stick your head under the car and look at the pipe. It almost def sounds like a clamp just slipped loose after installing it. Anything producing that much more sound will be visible. You may need to adjust the hangers for better fit.
It has been my experience if strange/different noises appear after some mods were installed is to start looking at those mods for source of the new sound(s). Even though it's been a couple weeks since those installations the heating/cooling (expanding/contracting) of those parts it's possible something needs retorquing. If the installation of these parts were DIY you know where you need to look/check for possible source(s).
Same thing happened to me once after installing my catback. Couple weeks later hit a bump or something and pipe came loose at rear section before muffler, car became very loud.
Glad you found the issue... with what you described I felt it would be something associated w/the mods recently done. Been there, done that... too many times. 😞
