Hum from closed (new) sliding windows

I don't know if this is the right place to post, but hopefully so! I am a renter (who of course just renewed my lease) and our landlord has installed new windows in the building. The new windows are double-paned but they let so much sound through! What I'm really trying to solve is this constant almost hollow-sounding hum (like a roar or rushing?) that comes from them only when they are fully shut all the way. It goes 24/7, it does not matter if it's windy or not, it NEVER stops. It's almost like a plane is flying overhead, that echoey sort of distant noise you hear, but it just never stops.

It's hard to tell where the sound is coming from, but I think it's coming from the "seam" in the middle where the two sliding panels meet. If I open the window, I just get regular outside noise. The street is quite far away and sure, there's some noise from it, but it's low-pitched and quiet. As I slide the windows shut, as soon as the two pieces in the middle start to overlap, I hear the hum. It's like the ambient noise is being kicked up in pitch. When the windows are closed and locked is when it's loudest, so I can only assume it's coming from maybe air or sound getting into the gap between the two windows? Right now there's just a strip of bristles and when I put my ear to it, I hear street noise as well as the hum, so I can't imagine it's airtight.

Does anyone have any ideas on how to soundproof this, or even if that's likely where the issue is coming from? I am not sure how to get any weatherstripping in that tiny gap or what is the best kind to use. I've even starting looking at DIY acoustic panels, but the window is 55x56 inches and I'm having a heck of a time finding a piece that large, not to mention the cost (I have four of these windows, all are making the same noise). I would like to try something else first to seal that middle gap.

Help would be so appreciated, I am going INSANE with this hum coming from the windows in every single room of my apartment. It's of course loudest by the window, but I can even hear it clear across the room. I can handle traffic noise, even if I don't love it. I cannot handle a constant hum 24/7 without wanting to tear my hair out, and it's only been a few days! They haven't even put the trim around the window yet, but the sound is coming from the glass region pretty clearly, not the frame.

Here are some pictures of the windows and two videos I took; it is really hard to hear and the hum sounds lower pitched in the video than in real life, but if you put on headphones and turn it all the way up, hopefully you can hear it. The second video shows the seam between the two sliding windows. (It's also raining in the second video, sorry!)

https://imgur.com/a/FdmJMWZ
https://imgur.com/a/nukdKvw
https://imgur.com/a/pxqjNOS