Question about Foo Fighters "Enough Space" intro

[asthenia15 62]

Does anyone know what effect(s) to use to get a similar sound to the first 12 seconds of the song?

[Benjirob 55]

Sounds much like a tremolo pedal to me, but could probably achieve a messed up sound like that with a delay pedal if you tweaked it enough.

[tom18222 49]

tremolo with an expression pedal controlling the speed