Well, having a separate sound file will be a challenge. beside the fact, that you'll always get the way louder base level of a computer room with it, it also depends a lot on the type and model of line printer. Equally important, the sound isn't much impressive as long as the cover is closed - yes, it did make a huge difference.

Maybe try this video The IBM 1401 mainframe runs "Edith".

Beside several printouts (sorry, always covered) including two very similar spaced but with different amount of characters printed, which is relevant for the specific noise, it also gives impression of basic sound level as well as card readers and keypunch in 'DUP' mode

Here are more, this time showing the printer without cover, but different cameras and different loudness setting. Not the basic noise the chain i making when the printer is in ready to print.

I think it would be a good idea to take a look at the 1403 printer manuals as they not only provide basic estimations about printing time for a line, but also take form advance according to form control into account - plus describing the allowed processing time for the CPU to feed the next line. A perfect line printer emulation would also have to include this part. This includes as well the I/O load on a given channel - don't we all remember printers having hiccups on machines with too many devices on a channel, just because the owner didn't want to buy more?