Squeaky sound from gas tank area, fuel pump or something else?

[queequeg]

It's a cyclical squeaky noise, the cadence follows the throttle in park or when moving. It sounds like it's coming from above the rear axle or gas tank area. It's not an exhaust hanger or heat shield, at least I highly doubt it. What do you guys think?

Video below, pardon the surface rust:
New video by Matt Maczuzak