The best way to find issues is to use a test tone track and play through the frequencies while checking all over the vehicle as it will help pin point the location.
I take care of each area by using silicone sealer, foam, tie wraps, mat, etc as the area dictates to cure rattles and buzzes, sometimes some expanding foam carefully squirt into an area I cannot get to.
Silicone on mounting pops, thin bead between overlapping trim panels, etc.....will help those areas yet still come out easily enough if needed.
I have disks I have used for years but you can download tracks to your phone, etc and run it through the audio system.
Sometimes noises show up in different climatic conditions so you have to test during those times on occasion to find and cure them.
Cool thing is when all done and the right amount of deadening even a lower cost car car feel like a luxmobile as that is mainly the difference and why they make a killing on high priced models based on lower cost chassis