I have soundtraxx decoders in my LL 0-8-0 and Spectrum 2-8-0 (the “plug and play” ones for each model, I can’t recall the numbers) and, once the locos are stopped, all I get is the air pump as well. I guess this is why they are the low-cost decoders. A nice occasional hiss while they’re standing still would be nice.
I too was disappointed that the plug & play decoder for the 2-8-0 did not have a steam hiss, and a generator whine when the lights are turned on would’ve been nice too.