Rattling noise from under vehicle

[APR28]

My 2009 CX9 AWD Touring with 81K miles has developed quite a loud rattling noise. The noise itself sounds like a loose heat shield and is accompanied by what sounds like a humming noise from the rear brakes rubbing. Because I cant pinpoint the sound I could be totally way off. The sound is definitely silenced by having the windows up but is louder going between parked cars and tunnel type places. It has developed a slight burning smell oily/rubbery but only outside and not in the interior if that helps. No burning smell through the vents. Car is not leaking any fluids and never has.

Some history: Front brakes are brand new and oem; rear brakes were changed a year ago with aftermarket rotors and pads and never seemed 100% perfect. They always squeaked in early morning/dew/rust situations and the rotors always stayed rusty. The car always starts off fairly quiet then the rattling gets progressively worse as a I drive longer. I originally thought it was a heat shield hitting the backside of the rear rotors. The rattling stops when I make a complete stop. The rattling is present when I let my foot of the gas

Attempted fixes so far at dealership that is stumped( Theyve had a sickness go through the Mazda dealership so they are short staffed so I think they arent spending enough time diagnosing)

checked rear brakes/knocked rust off---seem good(not 100% sure though)

replaced front brakes---noise still present

 

[astriuminc]

did you check wheel bearings ? it's a common problem with the CX-9

also, looks like you have a 2009 AWD with 81K miles, did you ever check the oil condition of your transfer case? members have reported rattling noise prior to failure.

 

[APR28]

I had the transfer oil changed somewhere between 40-44k.

At take off 1-10mph) the wheel first sounds like a really worn brake pad grinding. Between 10-30mph there is a fairly loud heat shield type rattle noise. After 40mph the noise becomes a very subdued rattle/hum. Upon coming to a stop, a burning smell comes in from the outside of the car.

 

[avidien]

I had the transfer oil changed somewhere between 40-44k.

At take off 1-10mph) the wheel first sounds like a really worn brake pad grinding. Between 10-30mph there is a fairly loud heat shield type rattle noise. After 40mph the noise becomes a very subdued rattle/hum. Upon coming to a stop, a burning smell comes in from the outside of the car.

do a easy and quick check of the AWD propeller shaft mount, see video below, if it's worn it would create the rattling sound, and if the rubber is worn and rubbing against the metal bracket, it will cause the burning smell inside the passenger cabin.

 

[APR28]

A heat shield on the gas tank was rubbing on the drive shaft. I looked around under the car and found nothing and so did the dealer. The lead tech who was sick last week takes my car in today and finds it in 10 minutes. No charge since they were guilty of not finding it last week.

 

[frmby97]

I have a 2011 CX-9 with the same problem I think. Except from what I've seen it looks like everywhere the heat shield attaches is broken. I think they would have to remove the drive shaft in order to replace the heat shield. Not sure how long that would take, or the price. Wondering about just trying to cut it out or pull it out and go without. Thoughts?

 

[ivanhoe67]

I had a similar "rattling noise", especially when the vehicle had been driven and was hot. We noticed it more when we pressed on the accelerator and put a load on the car. I put it on a hoist and started tapping with a rubber mallet. When I hit the muffler, I heard the rattle. There are different layers of thin sheet metal making up the muffler. On the bottom side of the muffler, center mass, I could push up a little bit and bend the thin metal and make contact with the inner part. I used a large clamp and a short bolt held in place on the center "weak" spot. The clamp squeezes the bolt to compress the outer sheet metal and therefore stop the rattling.