So yesterday my friend and I installed the new set of Berk HFC's on my Z.
Did the reprogramming with the gas pedal and all that as well.

But when driving around 2.5K RPM there are some vibrations when going through that low rpm band.
as well as when I engine break or down ****. I feel like my seat becomes a massage chair And Im hearing rattles of something loose in the dash now hah.

Is this normal and something I have to get used to? Or is there something else it could be?

I searched on the forums for any similar issues and couldnt find anything

 

Probably just rubbing somewhere in the exhaust on the subframe or something. Exhausts can sort of shift around on the hangers a bit when you are changing things. Get on a lift and rev it with someone underneath the car to pinpoint it.

 

More than likely it is hitting the factory heat shield. I had this issue and once I narrowed it down I just got a pry bar on it and bent it some