Help with flutter

I've watched the videos over and over... I feel like I'm doing the things you are teaching but my flutter sounds different than yours.

I would describe yours as a mellow undulating pattern of single note and chord... mine is a much less subtle slap like shift between the single note and chord.

This is the first technique I've hit that has stumped me... if I could even accidentally reproduce the right sound I think I might be able to figure it out, but so far no luck.

Any advice?