fluttering noise
 

I have 05 wrx and when i get up to 6k rpm or over I hear a nasty fluttering noise and i dont know where its coming from. Before this problem I got a po546 DTC code and I believe my car was put into safe mode b/c after 4k rpm I experienced alot of power lost, kinda like if I had to much fuel going in or it was bogging.

I am not receving any kind of code with this fluttering noise, please help me.