That's the last time I buy a Perrin product
 

Bought the Perrin catback a few weeks back after listening to many sound files over and over and deciding I liked it best. First one got damaged in transit and Quantum took care of me and the replacement arrived yesterday (not Perrin's fault, I know). So, I set about installing it lay on my back in the garage with the back end on Rhino ramps. Not the ideal way, I know, but it works. So, got the old cat-back off and went to install the Perrin mid-pipe. Wouldn't fit. WTF! Thought I might have bent the studs when I took the old pipe off so I layed the 2 flanges (new and old) end to end and compared holes. The Perrin holes did not match the stock holes and were of by about 1/8". I'm guessing you need a titanium tipped bit or something to drill the flange because my drills wouldn't. Ended up having to take it to a machine shop to get the holes widened so I could actually put it on. That's BS in my books. Wonder if anyone else has had this problem or I just got lucky?

Nope you're not alone, same thing happened to me. I end up taking the bolt that was attach to the cat and that was a pain and put new nuts and bolts. They don't even provide the bolt to the muffler hanger, aside from that everything went well.

After all that I realised that they actually sent 5 nuts & bolts, so I'm wondering if they expect you to remove the studs out of the cat and use their nuts & bolts? That's pretty crappy if they do. The 5th bolt, I assume, was for the muffler hanger but it's about 1" too short to be of any use. This isn't a cheap exhaust system either so I expected better. Does yours drone pretty bad at 70ish in 5th? Does the drone go away?

Nope it's here to stay, U can eliminate that if U put a small resonator. I believe Magnaflow makes one bout 14" long 3"internal pipe.
Have fun with your Perrin.

My friend had the same issue with his Borla on his 330ci. I think it's all about manufacturing quality. We used a grinder bit (composed of what I don't know) to widen the bolt holes.