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.

[Chamberpains]

Sounds like a harmonic vibration and probably nothing to be concerned with. Does it do it at any other rpm?

[Lonestar10]

Can't hear it at 775 idle but both my 900 and 1100rpm high idles do it

[Mattman]

I have a 2350 at about 900rpm I don't like the sound it makes. Seems like it is in a unbalanced state.

[hhow55]

Might be the turbo doing a cleaning cycle

[Lonestar10]

Could be idk just seemed out of place. Next target I'm going after is why I get a noseful of crank case fumes every time I use engine brake to slow down. Used to think it was valve stem seals but now with new head still does it. Maybe a turbo seal but I would think over a year of it I would think the bearings would have dynamited. As it barely has anything coming out of crank vent at idle but idk under load. Can't catch that perverbial tail I'm chasing.

[Rawze]

flex-pipe behind the turbo not installed properly / cracked? - seen that a hundred times on prostar.

[Lonestar10]

Could be cracked hard to tell since it's the woven wire style

[Chamberpains]

Smoke a cigar around the pipe and see if it blows away.