why does my 1998 lexus es 300 rattle from the front right side of my car

Could be a lot of factors that may have caused it to rattle, Might be your tires ( When was the last time you had it rotated? ). Could also be your brakes are worn out ( When was the last time you had them checked?) Could also be your rims and it also might be your steering.
In short, have it looked at just to be safe.

its an old car, old cars rattle and stuff.

Well l will say it can be one or more of the HEAT Shields on or around the exhaust system. it can also be the Catalytic Converter.

Overall you should get it checked out in person at your trusted mechanics shop.

Does it mostly rattle when you go over bumps. This sounds like a strut support which usually give out on the rx300 and es300 models.

probably ur tires. check make sure nothing got stick on ur tires.