Update: So, the grinding now happens when idle in reverse, however, same situation, goes away completely once warmed up. Went downstairs today and let it sit at idle for 20 minutes, same result, no grinding noise when allowed to warm up. Double checked oil and transmissions fluid levels. All good and clean. Waiting on my mechanic to come out in the AM this week to hear the noise at start up. Will try to remember to keep this updated for anyone who has simular issues in the future.
I have a 2012 Mazda cx7 fwd, auto, 4 cyl (not a turbo) at 215k that recently started making a grinding noise whenever I turn right, or back up durning acceleration ONLY. But heres the kicker; after about 10-15 minutes of driving her, the noise completely goes away as if it was never there. 0 evidence of the issue (which has made it hard to show a mechanic as theyre all 15 mins away from us). Tired recording it but it hardly comes up on my phone for some reason, despite it being clear as day.
The sound is definitely coming from the front right and can only be heard in the cabin, not the outside. So its made it hard to show our mechanic. However he took a good look under the car and saw nothing of concern, tested the tires with a crowbar etc. Fluids are all fine, level, clean with no evidence of leaks, no engine knocking or issues, shifts gears like butter, idles quiet, purrs like a kitten otherwise.
Any thoughts? I am getting a second opinion but have to wait a little so just looking to mentally prepare myself for the worse but hope for the best.
You are probably going to have to drop your vehicle off so the mechanic can drive it, maybe multiple times, cold or how ever long it takes it to make the noise, after being driven and stopped again… Also finding a shop with mechanic ears will help, most should have some or get them one…
Again, you might need to drop it off for a few days…
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Agree with @davesmopar
Based on your description, it may be the brake pads and rotors rusting a bit at night making the noise. Once you drive it a bit the rust is cleaned off and all is quiet.
Yes, but I think that a failing CV joint is also a possibility.
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Bit of an update: It now does it when shifted into reverse at a stand still, but again only at cold start. After 10 minutes of driving, no noise in reverse gear or turning etc. Does that chance things a bit? I keep reading Transmission/Gearbox but I have no other evidence of that like fluid leaking, low levels etc. I’ve driven/owned many cars with bad trannies and their symptoms never “went away” after a few minutes of driving. Could it be age/the cold? I park in an underground garage (Although I do live in a moist climate that rains 6 months of the year) so that’s strange to me and it’s never acted this way in the cold before but it did just start when the temps dipped. Just hard to pin point with so many factors. My mechanic has agreed to come out early this week in the AM to try it himself at first run of the day, which is great!
Hope you don’t mind if I still probe your brains however.
Thanks for your help and response!
Yes, that eliminates the brakes, steering and suspension for the most part…
Possible motor mount and or a pulley rubbing the frame or something…
Please keep us informed
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I just went downstairs and ran the car for about 20 minutes in it’s parking spot. No grinding after warming up, turning or in the reverse gear. I don’t know if that changes anything too?
Regardless will do, I’m curious as to what the cause is and will share once I do find out!
Do you have a CEL on (check engine light)???
If so what are the codes?? If not then NVM… lol
Could be power steering noise or transmission noise. If the pitch changes when turning the steering wheel or shifting from park to R/N/D, this might give you an indication of the source or the noise.
So no noise when engine idling, brakes applied, stopped in neutral; but when shifting into R, still stopped w/brake applied, the noise appears? & only immediately after a cold start? hmmm… I’m guessing some sort of transmission problem. The transmission has a pump that supplies very high pressure fluid to the transmission’s internal controls. High pressure is needed to create enough force to move the transmission’s various internal parts into alignment. You’re probably going to have to find a good transmission shop to assess the situation. Your transmission probably has several test ports the shop can use to measure the internal fluid pressure. The fluid pressure might be lower on cold starts b/c the parts that seal the fluid paths shrink when cold, and that small dimensional change could cause them to leak pressure internally. As the fluid warms up, the parts expand and seal properly.
If this is the explanation, ask the shop if a routine transmission service is worth a try. Fresh transmission fluid contains fresh seal conditioning chemicals, and might be enough to get it working again for a while at least.
When my truck’s automatic transmission developed a similar symptom , no grinding noises but wouldn’t shift properly when cold, it was in the shop for a complete transmission rebuild within a week. Expensive, but that fixed the symptom completely.
That’s my fear. I’ll see what my mechanic says whenever he gets the chance to come out and hear the sound and go from there. Fingers crossed it’s not, hopeful thinking that at worse, a trans fluid change will help it along (Been on top of that all her life with me and shes due in 10k anyways), but expecting she needs a major repair. Sadly, I’d just say I’d get a new car but it seems like in this economy, it’s cheaper to fix the transmission than it is to buy even a used car. Which is a catch 22 for me, while no one wants to spend thousands on a high mileage car, she’s been the most reliable vehicle I’ve ever owned in my driving life. For a car that has never given me a headache and only small billed repairs and cosmetic fixes, I don’t think I can me mad.
Thanks for your insightful response 
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Update and Resolution:
It ended up being the right front motor mount and the upstream air fuel ratio O2 sensor. We also replaced the PCV valve for good measure since it’s never been replaced.
Oil depleted suddenly, CEL came on after to indicate the O2 sensor went. However prior only the motor mount seemed to be the main culprit for the noises.
Running like she’s new again. Thanks for all your insights!
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Sounds familiar… lol
Glad you got it figured out…
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Good for you. Glad it was the motor mount, and not the transmission.
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