I've just clocked 178,000kms on my cx7. Bought brand new back in 2008. Never a problem, until recently.
Turbo sounds whiny when I step on the gas, and random white smoke when I sometimes takeoff from idling at the lights. Smells like burnt oil. Mazda service have checked it and confirmed it's the turbo, however they said it's still ok and so no need to replace at this stage. Service said that the age of my car and the kms may have caused this, and so what is occurring is that at idle the pressure builds up under the rocket cover and affects the turbo. At least that's their explanation. Possibly the following have affected it.....
A year ago I was made aware the sump seal needed to be replaced on my next service.
I neglected to go back for a year...
Then 4 months ago my street was flooded after heavy rain. About 3 foot high water. It cleared several hours later. I jumped in the car and drove it until smoke appeared in the cabin. We pulled over and found twigs, leaves, grass, etc in the engine bay due to the flood. Went to an auto car wash and blew all of it out.
I also drive my cx7 hard.
So, five possible reasons my turbo is sounding as it is.
1. Did not service regularly
2. Did not change sump plug seal (it is a slow minor leak they tell me)
3. Age and kms
4. Engine bay clogged with twigs, etc
5. Driving it like a race car driver
I don't want to sell it. So I will buy the turbo and do it myself.
Get the sump plug seal fixed
Clean out the rocket cover
Hopefully get many more years .
(Incidentally, Mazda advised me I could upgrade my rocket cover.