Regular Drone or Exhaust leak?

[Aceway]

I bought my 2008 135i a couple months ago knowing it had a somewhat sketchy history and I've been slowly fixing all the issues. The issue I've been trying to fix for the last week has been this terrible drone sound at low rpms.

I thought the problem may have been the berk exhaust I replaced with a rpi system but the sound still lingers. I've replaced the downpipe to midpipe gaskets but that didn't really make any difference. I installed some hybrid turbos a few months ago so now I'm wondering if maybe I didn't tighten the v bands enough. The sound was there with the stock turbos so I'm not too convinced it's the v bands.

Anyone have an idea of where this sound is coming from?