Exhaust whistling at WOT and engine flapping-ish sound - any ideas?

[Gambeez]

Hey guys, so this has been a problem I've been dealing with since I did my muffler delete last year.

Last year I just did a standard muffler delete with a single outlet dual tip. Whistled like CRAZY at WOT.

Recently I had a shop fabricate a custom quad exhaust, it's still giving a bit of a whistle but it's not as bad as before. I can actually go WOT without it shattering my ears. But it's still concerning, since I figured it might have been something with the previous muffler delete. But now I find it hard to believe that's the case since it's shown up again.

Any ideas what could be causing this?

Also, another clip I have coming forward, I've noticed this odd sound coming from the engine bay. I do have the disa/3 stage intake installed. I'm thinking this might be the disa valves, but I'm not sure if this is a normal sound I should be hearing or if one needs to be replaced? It's feint, but you can hear it around the 3/4 second mark if you listen closely.

Thank you!