Surging but not surging?

[Lonestar10]

Truck at high 900rpm idle does a normal idle noise then for maybe 4-5 cycles kind of acts like a surge but rpms don't move. It's kinda like it fires all the cylinders 1 right after another type sound you cant really hear it in the engine it's more or less it's more in the vibration it sends through the exhaust. I can somewhat replicate by barely tapping the accelerater over and over. Only difference is I make rpms move.