Longspur rattles are similar to each other. I find it useful to think of the notes of the Lapland Longspur rattle as being similar to the alarm call of the eastern Winter Wren (June, AK).
The Snow Bunting rattle is mellower and lower. Flock taking flight, also with buzzy calls (Jan, NJ).
buzzy flock call
probable alarm call at beginning of cut
The Smith's Longspur rattle is higher (June, AK).
McCown's Longspur has a squeaky rattle.
Two Lapland Longspur calls (by males) I recorded on the breeding grounds in Alaska were a three-parted jer-hu and a buzzy call, also three-parted, described as foraging calls in BNA (June)
A less commonly heard call by Smith's Longspurs is an Eastern Meadowlark-like buzz (there is also a clear syu). (Jun, AK)
The common Chestnut-collared Longspur flight call is a cher-dee (bird in flight, May, ND).