Hello, I purchased a used 2000 lexus the rear passager tire has some noise. I just got new rims, and tires. it sounds like something is loose.. noisy over bumps like a loose bolt.. could this be struts

MOunts for what? Engine, Transmission, body mounts?

I am thinking that the noise is from a failed wheel bearing or possible cv joint failure
find yourself another service dealer as tire noise is either there or not there and rotation (if it is a faulty tyie ) would move to the new position
Here is a clue to consider
rotating tires is a ploy by the tire dealers to sell tires
have a wheel alignment done on the rear first and then the front and leave the tires alone
if it is a front wheel drive vehicle you will get 3 times the mileage out of the rear tires compared to the front drive tires and that is a big saving for you
next point -- radial tires continue to wear in the same pattern regardless of where they are put so how are you to know it it is a faulty tire construction or a need for a wheel alignment
third point --- many brands of tires are made as directional tires ( a directional arrow on the side wall) and cannot be rotated because they cannot be fitted on a wheel that rotates against the arrow
if they are the wear in pattern of the belts in the rubber is altered and may lead to tire failure ---the tread pattern is designed to remove maximum water and produce maximum grip in the direction of the arrow

make sure that the inside of the rim is tight on the hub and not sitting off it
loose/ incorrect wheel stud nuts will also cause the noise

could be the wheel bearing, first check to see if the belts have shifte in tires, feel the sidewalls of tire for a buldge, also secondly switch front tire with back tire, could be the rim... if noise transfers to back then its rim..

I can think of two things not easily seen that can cause a banging when hitting small bumps;
The sway bar end links could be loose or broken.
The rear shock bolts, the lower bolt that holds the shock onto the rear axle, I've seen that mounting hole down there get enlarged, allowing the shock bolt to move about when hitting small bumps, causing a banging sound.
Check those two things out.

Could be tire noise, could be rear wheel bearing, differential (if rear wheel driven), or could be something associated with the brake.

Try swapping the tire with another tire. If the noise moves with the tire, it's the tire. If it stays, it's brakes (unlikely for the noise you mention), rear wheel bearing, or rear differential (lack of oil). Will probably need to have a mechanic to identify and repair.

struts are bad car can support 20 inch rims if struts are new if noise persist strut plate is rubbing

most probably a torn lower suspension arm rubber bush that would not show up if the car was on a 4 post hoist
there is a problem there as the noise would not be evident if there was nothing wrong
different tire pressures will give different noise when hit with a tire lever ( a trick used by truck drivers to check for flat/ under inflated tires
good tire solid sound
low pressure tire a dull sound

does the van shake or vibrate? does the van have tires on it ?start by switching the left rear with the right rear test drive and listen for soun if no sound then the tire has a bad steel belt replace tire if the sound is still present. jack up van and spin tire if no sound is heard replace wheel bearing and if there is still a sound look into brake drum for possible springs or clips that may have fallen into drum causing noise but i would say its more than likely the rear wheel bearing to change that u must buy a new bearing and follow instructions on replacing good