Oroad,
What year is your bike? 2012-2013 has the 3-intervenings when throttle is aggressively applied:
1.(((Sub-Rattle))) = Sounds like knock
2. Ign curve
3. Fuel pump cut
If 2011 and down, then back to low rpm, high vacuum at the IAP when the TPS opens past intervention or high vac pull. My guess is either or. If you have a late model, then sub-rattle I've been hearing before I locked the subs open. Now I hear zip.