Put shorter rear tires on my G37. Went from 26.7"(225/55/17) down to 25"(275/40/17). Would that much of a change cause a noise coming from the rear end or axles?

 

No. Its probably the tyres themselves

Think about it.
Your diff is spinning slightly faster per speed. Its not like your diff has never spun at that speed before with the old tyres.

Example with made up numbers...

If its spinning at 6000RPM at 70mph with your new tyres...

With your old tyres, it spun at 6000RPM at 75mph.

Either way...its not doing anything it hasn't done before.

If it whined at higher vehicle speeds with your old tyres....
It will whine at slightly lower vehicle speed with your new ones.

But if it didn't whine before...

 

What about the angle of the rear axle shafts?

 

That doesn't change with tyre size...

the wheel center is in the same spot. Diameter of the wheel or tyre doesn't change that.

Like...if you measure from some static reference point on the car...everything stays the same. If you measure from hub center to fender arch...it wouldn't matter if you had monster truck wheels or rollerskate wheels or no wheels at all. If the suspension compression hasn't changed and the diff mounting location hasn't changed...the axle angle hasnt changed. The diff is mounted to the car. Not the ground.


Besides...why would axle angle make the diff whine? The axle is bolted to a flange shaft and its a CV joint.

 

Thanx my man!! No matter the tire size the rear will sit the same and will center the tires. only ground clearance would be affected

 

No problem. Good luck finding the issue