Audio/Video problems

[RogerBear]

[This is a repost of an earlier query, so I could state the issue better and list the steps I have already taken.] PROBLEM: my audio/video quality has been declining over the past few weeks, manifesting as occasional moments of audio that sound rattly or overloaded. However, this decline has become precipitous in the last 36 hours, to the point videos or audios played on the computer have either intermittent sound or none at all. I am operating 64-bit Windows 10 on an HP ENVY computer bought in 2020. Until I added the sound card (see #2 below), I made no modifications. 1. I asked myself if it has to do with the SOURCE, the OUTPUT, or in the COMPUTER: • It happens equally when playing from YouTube, DVDs, CDs, or MP4s I've made myself, so the problem is NOT THE SOURCE. • It happens both with headphones and my external speakers, so the problem is NOT THE OUTPUT. • I conclude it must be SOMEWHERE IN THE COMPUTER. 2. My next question was whether it was in the SOFTWARE, HARDWARE, or SYSTEM: • It happens whatever program I use to play (the various options you can select by right-clicking and choosing "Open with"). They all produce a burst of sound, then freeze both video and audio, then hiccup and do the same again. The one exception is VLC, which plays the video smoothly for a while, but with NO sound; but even that begin to hiccup after a while. I I think this is probably just that VLC uses a different technique to cope with degraded input. Anyway, NOT SPECIFIC SOFTWARE. • I installed a new sound card, which did not help at all, so NOT SOUND CARD. • So I conclude it must be SOMEWHERE IN THE SYSTEM (by which I mean the CPU and the environmental factors essential to its smooth operation). 3. My next step has been to check on those environmental factors: • I ran a security check, and did not find any malware. • I used the Windows program to check the RAM; no problems. • Looking at the Task Manager, I did not find any drains on resources beyond the minimum. • Using various programs, I checked for updated drivers, necessary updates, registry errors, and so forth; these have supposedly now been fixed. With that, I'm stuck. But at least I feel better for having eliminated this bunch of things! Does anyone have any ideas?

[RogerBear]

For some reason, HP omitted all the line breaks in the above post. Sorry about that!