Mysterious screws - Need help identifying them
 

Yesterday I found two screws in footwells of REAR seats, one on each side. And could not find where they came from.
Also I noticed rattling sound from behind the seat / rear shelf area, when playing bass heavy music.
I have serious suspicions that these 2 things are both connected to each other.

Screws look like this!
Please help to figure out where they came from before I tear apart whole interior to find out! Thanks! :D
https://cimg1.ibsrv.net/gimg/www.clu...c209da325d.jpg

check if the factor sub is loose, they are new to me. What year if your car?

Yeah, I already checked the subwoofer mounts. (almost broke the cover).

Car is pre-facelift second gen, 1997.

Oh i just noticed that the screw in picture looks really big!
But actually its pretty small! The head of the screw is about the size of a nail of a pinky finger.

This type of screw is always used in bolting down the center console. Check the side of your center console and look for missing screw. It's also used on splash guards.

might not be from your car...most OE screws (not bolts) have a Philips head on it on top of being a 10mm hex head. that to me looks non-OE.

Thank for all the suggestions!

But it seems I have found the source of these screws. The back panels of front seats mounts with hooks on the side and metal ears behind lower edge with holes for screws, 2 on each side.
So it seems I've have lost 2 screws.

Subwoofer area is still making annoying sound, so I will still have to remove backseat when it gets warmer, up here.

Definitely not factory Toyota screws. So from what - who knows?

As for rattling from the subwoofer - well, I'd suggest making a CD of some low-frequency tone (e.g. in Adobe Audition), then looking in the trunk while it is playing to see if you can identify the cause. It could be the drive unit itself, of course.