On the s-10 Blazers I'ved owned the "morning roar" was caused by the radiator cooling fan kicking in. It's a viscous fluid clutch and many a morning it would roar for half a block.
It would also kick in in stop and go traffic with the AC on. Nothing to worry about just the fan working like it's supposed to.
My H3 has done the samething a couple of times. Just makebeliev it has a set of wings and can fly.
