No question here, but documenting a resolved rattle in my 2020 RX350 in case others have a similar issue. My vehicle developed a rattle in the driver door. It would generally only occur when driving on rough pavement, like the concrete streets with expansion joints in my neighborhood. I finally isolated it to the seat belt height adjuster. Pressing down firmly on the the top of the adjuster seemed to make the rattle disappear. I took it to the dealer, and just told them it had a rattle in the upper portion of the driver door. They, too, diagnosed it as the seat belt height adjuster, indicating it had excessive play.

They replaced the adjuster and that seems to have done the trick. I've driven it a couple of days with no more rattle.

 

Interesting as I have rattle I thought was from the door or B pillar. I will check the adjuster next time.

 

If the belt adjuster has excessive play, would tightening the bolt fix it?

 

I can't tell. It appears they had to remove the B-pillar cover to replace the adjuster, although I'm not certain of that. I had them fix it during the 10K mile service visit.

 

Good news and bad news regarding this rattle. The bad news is the replacement of the driver-side seat belt adjuster did not resolve the apparent B-pillar rattle. I thought it did, but it returned within a few days. Additional bad news is that I took the B-pillar apart twice and did thorough insulation, and it still didn't fix it. I also took the driver door inner panel off and did thorough noise insulation on it, too. The problem remained and my aggravation level was high.

Resolution
It turns out the problem wasn't a rattle, even though it sounded like it. The root issue was friction with the rubber weatherstripping around the door. I resolved the problem by thoroughly cleaning the door and body-mounted weatherstripping, wiping it with isopropyl alcohol, and then wiping on WD-40 Fast Dry Silicone Lubricant. That did it; I've driven it several days and the noise is gone. We'll see how long it lasts; maybe a one-time application is enough, or maybe not. It's no big deal to reapply occasionally, if necessary.

I found the root cause in a fit of frustration. After spending a couple of hours taking the door panel apart, insulating it and then reassembling it, I was very irritated when it made no difference. The noise mostly occurred when hitting concrete expansion joints and other sharp bumps at low speed. I had my wife sit in the driver seat and, with the door closed, I pulled up sharply on the door from the bottom, trying to simulate the vertical force of hitting a bump. Sure enough, my wife could hear the noise, seemingly toward the top of the B-pillar. The door is not loose, so the only thing I could figure was very small sliding forces on the weatherstripping created inordinately loud noise. A quick silicone application and subsequent silence told me I was on the right track.

This sort of thing is not a commonly reported problem with RXs, as I later discovered that it is with some BMWs. Still, if you have a door rattle that you can't find, trying cleaning and lubricating the weatherstripping with dry silicone. The side benefit of all my effort is that the door panel insulation made a noticeable improvement in the door closing "thunk."

 

You got any pictures of where this weather stripping was rattling ?

 

Wow -- great job of troubleshooting!

 

Take a look at these two photos. The blue line indicates the part that I cleaned and lubed with dry silicone. Note that I did this around the entire circumference of the opening, not just what is shown here. The noise, though, seemed to come from the upper rear corner; hence the reason I thought it was inside the B-pillar. I found doing subsequent research that some BMW owners place low-friction clear tape where rubber seals meet metal. I did not do that, but the dashed red line indicates where that tape would go if it would become necessary.

 

Ha! Thanks. Sometimes stubbornness is a decent substitute for intelligence....

I spent the first part of my career doing IT support and consulting for a large OEM. During that time I defined "Bamalam's Law" that states: 80% of all IT problems are solved in 5 minutes. Figuring out what to do during those 5 minutes can take hours, days, weeks or months..." I guess it applies to some non-IT things, too.

 

I like to think of it as "perseverance". LOL But I think you are correct.

 

Nextzett Gummi Pflege Rubber Care Stick is what you, and everyone who have this issue needs. Awesome to apply to rubber ones a year.

nextzett 91480615 'Gummi Pflege Stift' Rubber Care Stick - 3.4 fl. oz
I find it way superior to silicone lube.

 

awesome, and thank you Bamalam! i got a few clicks occasionally from that B pillar and this might just be that.

 

This is very helpful, @bamalam (aka fellow WV member )! Thank you! I have heard that Shin-Etsu silicone grease is excellent for this. Honda's part number is 08798-9013 in case anyone needs to quickly find this.