Ever since I replaced the center resonator with an x-pipe, I've noticed an issue under very specific conditions.

Under acceleration in high-gear/low-rpm, there is a chattering noise from the exhaust and the car sort of surges ever so slightly (occilates between accelerating and coasting). I can correct by shifting down or applying a lot more throttle but just wondering if this is normal and if anyone else has experienced it? It was definitely not there with the stock exhaust. Thanks.