Yesterday I jacked up my 2006 AWD IS250 to install side splitters. The next morning on my way to work I heard a clunking noise from the passenger rear. Almost like a loose strut tower. I've been running Godspeed springs for about 4 months and that corner has been a little louder than others but this time it was much louder.

The noise would be constant under acceleration but go away when coasting and could only be heard over bumps. I checked the splitters to make sure they were not flapping while driving, there was no play in both splitters. I jacked up the car and pulled off the passenger rear wheel to check for any bad bushings or ball joints, they all checked out. Tore apart the trunk to check the bolts on top of the strut tower, they were all tight. Even checked all the bolts on all suspensions components, all tight.

Next, I put the wheel back on and put the car in Neutral turned the wheel by hand to check for any noise from the drive shaft, no noise. CV boots are not leaking or torn.

Held the wheel while on the car at 9 oclock and 3 oclock position to test for play, none. Tried the same at 12 oclock and 6 oclock, no play. I am running adapters and checked the nuts for those, they were tight.

Eventually I put the wheel back on and had my brother drive while I sat in the rear passenger seat. I could feel the clunking directly underneath my feet. My feet were not near any suspension components. Same symptoms, clunking under acceleration but silent when coasting.
We drove around for a bit then eventually it went away (after the engine warmed up). Under modest acceleration you could not hear the clunking but under WOT you could hear the clunking for a slight moment.

I haven't driven the car yet when the engines cold because I literally just got back from the drive. I did notice that the exhaust is resting on this metal crossbar. The section right before the 2nd resonator. See pic below. My question is: is the exhaust supposed to be resting on that bar like that?

 

Negative Captain. It should be suspended by rubber touching nothing except the connection to the heads. Likely missing some hangers in the aft section.

While under there for the next go round make sure the rubber in the center section of the driveshaft isn't falling apart too.

 

Look for this hanger. Likely missing or torn on yours.
Glad mine isn't all rusty like that....

 

Minnesota winters are rough. You should see the rear control arms.

Ill look for the hangers and check for any heat shielding as well. Thanks.

 

Check your CV axles. I had an annoying clunking noise before with similar situations and the CV axles were shot and slinging grease

 

I know my post is long so you might've missed it but I already checked the axels. Rear CV axels are fine. No tears or rips.

 

The weirdest thing about this is that it seems to go away when the engine is warmed up. I know metal expands when heated so maybe the exhaust has expanded on enough to lay and cover more surface area on top of that bar, thus reducing the noise? When the engine is warm and under WOT the sound is slight but still there.

Another possibility is the CAT converter going out but how would heat affect the CAT to reduce the noise?

 

Sorry I was at work so it was a quick read over. hmmm...

 

Or when cold and doing a High Idle speed the torque from the engine lifts the pipe?
Maybe?

 

The issue's been fixed. The exhaust was hitting the cross member in the pic I posted. While getting my muffler deleted the guy bent the cross member down a quarter inch for clearance. No more rattle.

Now I gotta fix the cabin drone around 2k-3k rpm. Lol.

Thanks for your input guys.

 

You shouldn't have done a muffler delete. A lot of people who do it chasing sound regret it later. The only way to lessen the droning is a resonator, either a Helmholtz or Vibrant makes a 2.5 and 3.5 Ultra Quiet straight through resonator. Since you have stock piping it would be 2.5"

 

IIRC stock diameter is 2.25. Anyway, i still have my oem resonator and it still drones from 2k-3k RPM. Would you reccomend replacing the OEM resonator with the Virbant one or keeping the OEM and adding an additional vibrant resonator?

 

I would keep the OEM resonator and add a Vibrant Ultra quiet resonator. Some background: I had a 2018 Honda Civic Si, to get better performance, I changed the OEM exhaust with a 3" SS performance Cat-back. Great looking exhaust, aggressive sounding, but the drone was a killer. Long story short, I ended up having to install the Vibrant resonator. It reduced the drone about 50 percent, making the car more liveable. Below are some pics

 

IDK if i have room under there. Might have to delete one of the cats.

 

You can also try a helmholtz resonator, they are installed alongside the pipes and don't take up as much room