A small DMA transfer is not unusual for SB detection / initialization when games start up. It can cause an audible pop depending on the sample(s) in the transfer. The difference between SB16 and other SB types is likely due to the speaker enable state. My use of the word "speaker" here refers to a SB DSP flag, not the PC speaker. A disabled speaker flag doesn't actually silence output on an SB16, but it does in older models. You can probably see this in DOSBox debugger log messages where the init transfer is logged as "Short transfer scheduling IRQ ..." for sbtype=sb16, and "Silent DMA Transfer scheduling IRQ..." for other sbtype= settings.

ripsaw8080, thanks for the explanation. Very interesting! I guess as part of the detection, some games (or drivers) verify operability using the small DMA transfer.
(Reminds me of those $1 credit card charges (and immediate refund) used by some smaller websites just to check that the entire payment loop is valid!)

I wonder if these could be safely discarded? ie: if it's the first-ever DMA transfer and if the size is less-than-some-threshold, then discard it one-time-only.

I may have become relatively insensitive because there are games (usually not from big name developers, mind you) doing stuff during SB initialization that is much worse for the ears than a small pop. In any case, I can safely suggest not going too far with hacks. 😉

Good advice - and now that you mention it, I do remember some games really mangling the speaker on start up!
Around '93 I upgraded to a pair of speakers with a power-button on the front and wised-up to those games.. only powered on the speakers after the game was up 😀