2012 CX-9 Loud rumbling / humming when accelerating; vibration

My 2012 CX-9 is making a loud rumbling / humming when accelerating. I also feel a vibration in the steering wheel as well as the seat. Took it to the dealer and they said it was the motor mounts; had those replaced. Did not fix the issue. Now dealer is saying it's the muffler. I don't hear any type of rattle like you would expect with a muffler. The car has 68,000 miles on it. Anyone else had this issue?
 
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Mazda CX-9 Grand Touring 2016
Is it all wheel drive?...Could this be the rear drive unit failing, as they're prone to do?

When the car is taken in for repair be sure the service writer puts down the problem, not just his guess at how to fix it. If the problem is written down but not fixed, don't pay; take a test drive before accepting the car. You didn't get what you asked for. As for the motor mounts---ask for an appointment with the service manager, the boss of the department. Explain what happened, that you paid for something that did not correct your problem, and you want that much credit towards actually fixing what's wrong. Be calm, business-courteous, and firm. Check what auto repair laws your state has and come armed with the law and the facts.

My state lists as one unlawful auto repair practice: "Charging a customer for unnecessary repairs. For purposes of this subsection "unnecessary repairs" means those for which there is no reasonable basis for performing the service." Your motor mount replacement was unnecessary, and in my state unlawful.
 
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Is it all wheel drive?...Could this be the rear drive unit failing, as they're prone to do?

When the car is taken in for repair be sure the service writer puts down the problem, not just his guess at how to fix it. If the problem is written down but not fixed, don't pay; take a test drive before accepting the car. You didn't get what you asked for. As for the motor mounts---ask for an appointment with the service manager, the boss of the department. Explain what happened, that you paid for something that did not correct your problem, and you want that much credit towards actually fixing what's wrong. Be calm, business-courteous, and firm. Check what auto repair laws your state has and come armed with the law and the facts.

My state lists as one unlawful auto repair practice: "Charging a customer for unnecessary repairs. For purposes of this subsection "unnecessary repairs" means those for which there is no reasonable basis for performing the service." Your motor mount replacement was unnecessary, and in my state unlawful.
Thanks for the reply, PTguy! The good news on the motor mounts is that I only had to pay $100 for a deductible. I have an unlimited power train and Engine warranty on this car (should have been a red flag for me when I bought it back in December 2019). I do know Florida, where I live, has a Lemon Law that I've been looking into. Part of me hopes the muffler is not the problem because it is Strike 2 on the same issue. Yes, the car is all wheel drive. I don't know anything about the rear drive unit, tho. I am seriously NOT a mechanic.
 
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2010 CX-9 GT
If it's the muffler or exhaust you should be able to duplicate the sound/vibration at a dead stop by putting the car in park or neutral and giving it a little gas.

Is the noise only when you are accelerating or does it occur the entire time you are moving?

As mentioned above, the transfer case is a weak point of the all wheel drive system and could be causing this. Wheel bearings have also been known to fail in these cars, but that would be a more or less constant roaring/grinding noise when moving.
 
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If it's the muffler or exhaust you should be able to duplicate the sound/vibration at a dead stop by putting the car in park or neutral and giving it a little gas.

Is the noise only when you are accelerating or does it occur the entire time you are moving?

As mentioned above, the transfer case is a weak point of the all wheel drive system and could be causing this. Wheel bearings have also been known to fail in these cars, but that would be a more or less constant roaring/grinding noise when moving.
The noise goes away when I am not accelerating; so when I'm cruising up the highway, it's fine. Other than the vibration. It's at the dealer now so I am not able to test the park/ neutral and give it gas. I am going to be a pissed off customer if they replace the muffler and I'm still having the same issue. Then I will fall back on what PTguy said with the auto repair practice. Maybe I should just have the dealer try to fix it ....
 
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Mazda CX-9 Grand Touring 2016
Call the dealership right now. Ask for the service manager. Tell him that you need the problem you described added to the work order. You will not pay another $100 for another repair that does not correct the problem. Test drive the car before you accept the work. Read your warranty paperwork. I expect that a muffler is a consumable item you must pay for, but read the paperwork.

Florida law 559.920 Unlawful acts and practices.—It shall be a violation of this act for any motor vehicle repair shop or employee thereof to:
(4) Misrepresent that certain parts and repairs are necessary to repair a vehicle;
(11) Cause or allow a customer to sign any work order that does not state the repairs requested by the customer
(you did not request motor mounts or a muffler. You requested that the noise and vibration be corrected. The motor mounts were misrepresented as necessary to correct your problem. Perhaps also the muffler if the problem persists.)
http://www.leg.state.fl.us/STATUTES...ng=&URL=0500-0599/0559/Sections/0559.920.html
 
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Call the dealership right now. Ask for the service manager. Tell him that you need the problem you described added to the work order. You will not pay another $100 for another repair that does not correct the problem. Test drive the car before you accept the work. Read your warranty paperwork. I expect that a muffler is a consumable item you must pay for, but read the paperwork.

Florida law 559.920 Unlawful acts and practices.—It shall be a violation of this act for any motor vehicle repair shop or employee thereof to:
(4) Misrepresent that certain parts and repairs are necessary to repair a vehicle;
(11) Cause or allow a customer to sign any work order that does not state the repairs requested by the customer
(you did not request motor mounts or a muffler. You requested that the noise and vibration be corrected. The motor mounts were misrepresented as necessary to correct your problem. Perhaps also the muffler if the problem persists.)
http://www.leg.state.fl.us/STATUTES...ng=&URL=0500-0599/0559/Sections/0559.920.html
I'm on it! Already left a message with the Service Manager. I do need to know what they plan on doing if the muffler is not the issue, after I shell out $1200 (it is not covered under warranty). Thanks so much for the information!
 
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Mazda CX 9
Our 2010 CX-9 was experiencing a similar issue a couple years ago. The car would rumble and lightly shake at certain MPH and it would go away at certain speeds. The wheel would shake and you could feel something out of balance right beneath the center of the car. The dealer said it was a output shaft carrier bearing that lies between the CV axle and the output shaft of the transmission. Their price was well over $1,000 and I found the OE Mazda part online for $20. I did the repair in my garage and was disappointed that it did not fix the problem, yet relieved I hadn't paid 1K for something I didn't need. I took it to a Ford dealer and had them check it out. They said it had a stuck caliper and wanted around $400 to replace it with a new brake job. I couldn't believe a caliper could cause the rumble and vibration at the speeds and attitude of the car but when I was driving home I barely touched the brake pedal when the rumble started and it immediately went away. I found source of my vibration and rumble! Purchased a new caliper with rotors and fresh pads for around $100 total and the car is smooth as glass driving down the road.
 
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Funny yours turned out to be a stuck caliper - prior to the acceleration rumble and shaking, I had my brakes and rotors replaced. Got the car home and was driving the next day and the brakes weren’t working properly (not stopping all the way without pressing the brake pedal very hard). Took it back to the mechanic and they said they couldn’t find anything wrong. I had to drive the car with the mechanic with me to prove I was not crazy. He admitted that I had a stuck caliper but the problem ended up being a bad brake booster. While replacing the brake booster, they said they replaced the caliper. The rumble and shaking started after that so maybe they didn’t replace it? Car is still at Mazda so I will call them Monday.
 
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