Knocking from under driver's seat
 

My '07 RX has a strange vibrating knocking sound that seems to be coming from under the vehicle under the driver's seat. It's not the plastic gas tank shield as I've already secured that. It sounds like a rubber ball bouncing around in a bucket, so my first thought was that maybe the spare tire was a little loose and was bouncing against the underside of the car and the sound was just transferring to under the driver's seat. I tightened up the spare and then removed it completely, but the noise remains.

I've tried using a piece of folded cardboard to secure everything I could find under the car that has any play but have not been able to track down the source. The noise only happens while the car is moving and tends to be less frequent at highway speeds. I think it's originating toward the rear of the vehicle as it rattles more as the rear wheels go over speed bumps or into a driveway.

I'm really hoping it's not a suspension issue as the car only has 63k miles, but I'm thinking that might be the case. I don't want to start throwing parts at it if someone else here has had the same issue and knows how to fix it. Any insights are much appreciated.

Thanks in advance.

If you cannot find the source you can try two things, first would be to have someone drive around your neighborhood (or the closest place where the noise occurs) while you are in the cargo area. See if you can isolate it that way. Recommend you remove the cargo cover and the jack as mine bounces around due to a weak rubber retainer. If that doesn't work then find a decent shop with chassis microphones, have them hook those up and test drive it, they'll be able to pinpoint where the noise is that way which should point to the source.

All this assumes you done the basics - visual inspection underneath, load test ball joints, etc.

Good suggestions. Create a checklist, it helps.

when cold, spay part of car underside with water to see if that helps locate.

Problem solved
 

The problem was a bad rear strut. I replaced both rear struts and not only is the noise gone but the car drives MUCH better now. Thanks for all the suggestions.

Went through the same, replaced struts on Monday, what a difference with new quality rear struts. https://www.clublexus.com/forums/ima...ons/icon10.gif
Good to hear your issue was solved.

two rear struts 2009 RX-350 AWD
 

Did you have the dealer do the replacing of two struts...was curious as to the cost of replacing[two struts] as i think i'm about due...thanks

I replaced them myself. An independent shop that I trust quoted me about $540.

Same here, paid $501. Monroe Struts installed, reused the OEM Mounts that were in excellent condition.