Lexus ES

Check suspension parts for wear or looseness
Strut mounts, bushings etc.

If its a rattle on slow speeds while going over road imperfections try this:

Here is what i did:

I bought a silicone based spray lubricant (for metal to non-metal surface contacts) from O'reilly parts store for $3.99. I tried looking for this in Autozone but could not find it there.

Open the hood and from the top found the place where the strut mounts are positioned. Each of the strut mounts are on the extreme left and right side close to the passenger compartment just above where the tires are located. You can see these when you open the hood. Just look for 3 large bolts with a cup type depression in the middle with a central bolt. If you touch the inside of the cup, you can feel the rubber.
All I did was spray the lubricant near around the boundary between the inside wall of the strut mount and the round-shaped rubber piece at the centre of the strut mount. I sprayed a few times changing the position of the spray each time. Basic idea was to get some of the lubricant around the surface between the rubber and metal.

I did this first for the right side since that was where the problem seemed worse. After an hour or so, I drove the car and the noise from the right side was completely gone. I couldn't believe it. I could still hear the rattling noise from the left side.

So I repeated the procedure for the left side as well and the car was completely rattle free. It was an amazingly simple solution and worked wonders.

Here is my hypothesis on why it works: The rubber piece between the metal contacts acts as a dampener. When it hardens,

I changed mine 4 years ago. Very easy if you are handy with tools. I would do a quick flush on the cooling system. A can of "Quick 10 Min Flush" works fine. Add back water till it runs clean. Let it cool and open the petcock again and drain out what is left of the the anitfreeze (open rad cap to be sure none is held in because of vacumn. Next take both clamps on top that hold the rad inplace off. Then take out the bolts top and bottom that hold the rad in place. Then disconnect the upper hose, lower hose, transmission line. When it free just pull it staight up and out. Took me 15 mins. Besure you take the rubber gromits of the bottom of the old rad and put them on the new rad if they did not come with it. BESURE they are not down on bottom of the fram. (I missed this and it took me 2 hours to get the rad to fit because the gromits were missing on one side.) With both inplace the rad sliped in with no problems. Reconnect all hoses and clamps. If I hadn't missed the gromits, I would have been done in less than one hour. I paid $138 for the after market rad. I see they are now about $185. Replace with new Toyota antifreeze. (Better then after market stuff). BESURE to run the engine while adding the new antifreeze and turn the heater on high till it is filed. Let it run till normal oprating temp.This will get any air out of the heater core which is under the dash. If you don't you'll get no heat the next time it is cold. Hope this works. My email is denver6234@aol.com if any questions. No I do not work for Lexus or Toyota. Just a 67 year old guy who was too cheap to pay Lexus $750 + labor four years ago. Good luck.

I just replaced the radiator on a 1995 Lexus ES300, same process, followed the above instructions from Denver, other than he didn't mention of moving the fan system back toward the motor,and in the new Rad were the new tubing fittings for the transmittion hoses, Very easy to do, time frame for me, two hours. I bought new hoses, clamps, and antifreeze, should you need help, my email is clarkwilliam@yahoo.com.