Brake issue?
 

I started hearing (and feeling) a rattling noise, as if it was coming from the front driver side wheel. At first I thought it was the tire so I checked it, looks ok. I noticed, however, that the rattling stops when I press on the brake (it's loudest around 25mph, can't detect it at highway speeds).

Gonna jack up the car and take the wheel off. What should I look for?

Check the brake pads. Sounds like time to change the pads.

yea check them. idk if the supras calipers have the pad retention clips/springs. if they do, check to see if any are missing or broken. that would allow the pads to rattle freely inbetween the caliper and rotor.

The pistons don't back off enough for the pads to rattle if the springs are missing. They just help prevent the pads from dragging and causing unnecessary heat.

The piston has enough range to burn through even the metal backing of a pad... you'd hear grinding long before it would start rattling.

Check for a broken or cracked pad or rotor. Check to make sure all the glides are firmly in place and that the caliper brackets and the calipers are all firmly connected.

Don't discount the possibility of a damaged suspension component either.

definitely true ^^^ in most cases. had this issue with my truck. 20+year old brakes/calipers, old fluid, busted clip and a lil dust and rust. rattled like a SOB till i redid the calipers and pads. im prolly that 1 in 10 million, that is my luck lol.