Looking for ideas/thoughts on a sound I hear while driving the SS;

I recently installed the SLP LT's, Random Tech cats, SLP Y-pipe, and Loudmouth on the SS.

If I'm driving along, around 45-55, and accelerate hard, I hear what sounds like a "fluttering" sound, for lack of a better description.

I've contacted SLP and will be visiting them Monday. They said it may be that I have a good way of exiting the exhaust, but I need to improve the airflow into the engine. I have an MTI lid, and K&N, but they suggest I get a new MAF, and this may alleviate the sound I'm hearing.

Anyone have any thought/ideas?

Thanks

Ed