2007 Mazda CX-9 hums

I am hearing like a humming noise when I speed up it grows with the speed.

It might be the normal fuel injector sound. Seems possible it has been there all along, but so faint you didn’t notice. Until one day you did notice, & now you are hearing it consistently b/c only now you listening for it.

If the hum is a lower pitch, failing wheel bearings are a possibility.

+1
Or, this could be tire-related.
Are the OP’s tires nearing time for replacement, or were they recently replaced with a type of tire other than the previous tires?

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