After wasting a couple more hours on assorted computer maintenance activities, I still have clicks and pops in the ASIO audio output.
Being a little suspicious of the Yamaha mLAN bus, which is my usual audio I/O device, I hooked up an M-Audio Fast Track Pro USB and yanked the mLAN drivers entirely out of the system. I don’t hear quite as many clicks now, but they’re still there. Ergo, it’s not mLAN, it’s the CPU. Some background process is stepping in and hogging the CPU from time to time, causing audio buffer underruns.
I had a look through the long list of background processes in Task Manager, and disabled a few of them. God only knows how you’re supposed to do this — you can stop them from Task Manager, but I’m sure they’ll start up again the next time the OS boots. So I located the .exe files and renamed their parent folders with a _BULLSHIT. After a restart, I’m still hearing clicks and pops.
This is not supposed to happen in a modern computer unless you’re running tons of audio. Specifically, it’s not supposed to happen when the DAW’s CPU meter is at or below 40%. There should be plenty of CPU overhead available to handle momentary needs. But there isn’t.
I can probably reduce the number of clicks per minute by increasing the ASIO buffer size. That adds directly to the latency: MIDI-in to audio-out time becomes an issue if you’re playing a softsynth using a hardware interface.
I think I’ll just go play the piano instead.