Had the same issue. Magnaflow refuses to admit any flaw in the design of their exhaust, even though that's exactly what the problem is. I have since sold my Magnaflow. Trim the exhaust a bit where it mates with the OEM tubing halfway under the car. This allows the entire catback to sit "deeper" or further in allowing for proper drive shaft clearance.
Have you ever had a loud, metallic screeching sound while driving in heavy rain or snow? I think that's what causes this issue and it happens with the stock exhaust as well. Basically what happens is the water splashes into the exhaust causing it to cool and flex into the driveshaft.
Haha wow they refuse to admit it that says a lot about a company. Kind of disappointing. Thanks for the tips ill see what I can work out and hopefully get some clearance before it shreds a hole right through.
In regards to ehhh. No snow around here lol but definitely heavy rainstorms don't think I've ever heard any screeching during those times. I really only noticed twice so I pulled over checked then put pressure on the tips to push the exhaust down away from whatever it was hitting and that seemed to work but if it continues to happen it obviously needs a better fix.
The theory is that the cold water cools the underside of the exhaust which makes it contract, while the top of the exhaust stays hot and expands, so it bows upward and makes contact with the driveshaft. I've had it happen to me a couple times in heavy rain and snow and I got a really loud squealing noise. Volvo has acknowledged that the problem exists on their AWD models and their fix is to install an exhaust hanger that prevents it from touching.