Hey my friend's 7th gen civic coupe makes sort of a popping noise when turning and harder than normal accelerating. Could this be the axle or some other problem?

 

Sounds like a bad axle, though you also may want to inspect the upper and lower ball joints as well.

 

ok
He thinks that it is his exhaust because it started around the time he put it on. Could that be it?

 

We're left guessing unless you can supply more information. Where is the noise coming from? A popping noise really doesn't fit well with an exhaust problem.

 

well a axle is easy to see if its loose, just jack the car up and turn the wheel with you under the car... if you see or hear alot of slack in the axle shaft then its bad.

or test the balljoints to see if its the upper or lower balljoint or even the tie rods could even be busted bushings.
theres so many things that could be poping we just need more info of when does it do it and when does it not....
a combo or just a single item.
over bumps
turning
accelerating
stoping

 

Does the exhaust rub against anything?

If the exhaust has poor fitment and is rubbing against a heatshield or the chassis, it could cause popping noises. My old Civic used to do it.

 

Well, it's coming from the front drivers side of the car. I've heard what a bad cv joint sounds like and it sounds very similar to that when accelerating and turning left. Could it be the cv joint?

 

yep
replace the axle