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Discussion Starter · #1 ·
Hello,
I have a 2014 QX60 with 150k miles on it. The car has a loud idle from inside the cabin. The engine sounds kind of like an exhaust leak or a diesel engine. I get an occasional check engine light with the code P0420 Catalyst System Efficiency Below Threshold Bank1. The Catalytic converters are 1.5 years old, new O2 sensors, New Y pipe on exhaust, spark plugs 1.5 years old. My mechanic has said that the sound is not from an exhaust leak, but he is not sure where it is coming from without additional diagnostics being ran. I have also cleaned the MAF sensor, and cleaned the throttle assembly and PCV valve. If Iput my hand on the engine cover and the Air intake manifold, I can feel a vibration that matches the sound I hear in the cabin of the car. At this point, I am not sure what to check next. Does anyone have any ideas?

Thanks,
 

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It's likely the leak is coming from the new exhaust parts. While I'm sure you have an excellent mechanic, you should get a second opinion to be sure. Engine exhaust sounds are pretty distinct.

BTW, what causes you to get new cats at 150k?
 

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Discussion Starter · #3 ·
It's likely the leak is coming from the new exhaust parts. While I'm sure you have an excellent mechanic, you should get a second opinion to be sure. Engine exhaust sounds are pretty distinct.

BTW, what causes you to get new cats at 150k?
Thanks for the reply! I traded for the car and it had a bad cats the bank 1 and 2 cats were bad plus 3 of the oxygen sensors. I fixed that last year. Is it possible to have exhaust sound in the cabin but not outside? It sounds like it is right under the dash.
 

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Thanks for the reply! I traded for the car and it had a bad cats the bank 1 and 2 cats were bad plus 3 of the oxygen sensors. I fixed that last year. Is it possible to have exhaust sound in the cabin but not outside? It sounds like it is right under the dash.
Not in a normal way. There is a ton of sound deadening in the floor while escaping exhaust (before the mufflers) is extremely loud. It's not common to hear sound inside and not out. Try getting low or under the vehicle while someone else gets in and revs the engine. That may help isolate the location.

What did it cost to replace your cats? My bank 2 may need to be replaced.
 

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Discussion Starter · #5 ·
Not in a normal way. There is a ton of sound deadening in the floor while escaping exhaust (before the mufflers) is extremely loud. It's not common to hear sound inside and not out. Try getting low or under the vehicle while someone else gets in and revs the engine. That may help isolate the location.

What did it cost to replace your cats? My bank 2 may need to be replaced.
For both bank 1 and bank 2 cats, it was around $1,300.

I spent some time working on my car last night. I replaced the spark plugs and ignition coils. I feel like the car is a little quieter and runs smoother. I still hear the noise tho. I did some investigation under the car like you suggested.

While under the car with the engine running, I found that the fuel lines from gas tank all the way up to the intake vibrate. Is that normal? Also the exhaust vibrates at the same frequency as the fuel lines. Would one cause the other to vibrate? I did tighten the exhaust pipe bracket by the front cat. It was not rattling, but was definitely not as tight as i think it should have been. I was not able to check the tightness of the bracket bolt on the back side cat because of the path of the exhaust pipe. I need to figure out a way to check it, but with current tools I am not able to test tightness.

Any idea if it is ok for the fuel lines to vibrate? I have never touched fuel lines with the engine running, so I am not sure if it is normal, or and indicator of something to check.
 

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New plugs and coils shouldn't reduce sound unless there was a bigger issue like misfires (doesn't sound like you're vehicle has this issue).

Are your fuel lines vibrating and making sounds, where if you touch them the sound goes away? They shouldn't vibrate, given this, the fuel pump may push a slight vibration through the metal lines. It sounds like your lines are vibrating aggressively. Otherwise, the metal lines are further isolated with a rubber connection to the engine.

I'm curious about what's causing your fuel line vibration. I don't think I've helped, but please let us know if you find anything else.
 

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Discussion Starter · #9 ·
I didn’t either until I dug into the issue a little deeper. There are 2 dampers one for each side of the fuel rail. It was a cheap repair, both dampers were $40 on RockAuto. My car sounds better and runs a lot smoother.
 
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