The verse of Ava Adore is sung over a repeated F5 chord with a really cool effect. It definitely has some wha in it, but for the life of me I can't get the same sound. Any ideas?

I'm using a strat through a Marshall amp and an Digitech RP50 effect processor.

i think that's a synthesizer playing that, but i'm not sure. if it is a guitar, i'd say he used an envelope filter.