Greddy Exhaust Drone

dts3

sI recently installed my Greddy Evolution GT exhaust. It's a beautiful exhaust; nice welds/flanges/etc...

I love how it sounds on startup/acceleration/downshifts. My problem is that there is insane drone between somewhere around 2800-3200 rpm.

Does anyone else have this exhaust with this problem? I still have factory cats

A few things to note:

1) Everyone says the fitment on this exhaust is great, but that's not my
experience. The Y-pipe seems almost just a tad too wide. I had to loosen the cats to get it to bolt up (I tightened the cats back down). I'm fairly sure that the Y-pipe isn't upside down.

2) Even though they are centered vertically and horizontally, my tips seem to stick out more than other pics I've seen with this exhaust.

The exhaust doesn't make contact with any other parts of the car

Is this an install error on my part? Can it be related to my small problem with the Y-pipe? I'm out of the country at the moment and don't have pics, so I'll have to wait on that.

A bonus question:
This particular exhaust doesn't have any flex pipe. Given that I had to loosen/tighten the cats to get things situated, should I worry about things being too rigid?