I'm going to use the word "pop" to mean an individual clatter noise. "POP" is a loud clatter noise. "..." means no clatter noise.
It sounds like this at idle:
pop pop pop pop pop pop pop pop ... POP POP POP POP pop pop pop pop pop pop pop pop (so on, so on, with the pause and loud pops, etc., etc.)
The pulse is JUST sound, the car does not buck or surge at all.
Any ideas?