Mystery rod banging machine - GIF

[Toolmaker51]

Looks like Dave and TM51 are both correct. Rotary kilns use a similar technique though in the case of a cement kiln there are usually large heavy chains welded inside the drum as it rotates the chains called clinker chains clank against the inside as it rotates

Mine has clinker and clanker chains; lovely two-part harmony. Intended adding bongers and dongers for a non stop "Anvil Chorus", but that's just silly.
New project is figuring how to infect rappers with boils.
Guy in shop listens to a lame country music station, I mean HORRIBLE! Endless over-use of wallering slide and pedal steel guitars.
I ask him when someone is going to euthanize the alley cats...