------1-----
Try:

snd_async_fullyasync 1

See if it's any better. It might de-sync some of the dialog, but it should remove the stuttering.

Rick
Valve

------2-----

Getting the game to load as much of its self into memory as possible also helps a lot; to do this, right click on Half-Life 2 in steam and select properties, then click launch options, put in "-heapsize 256000" without the quote marks. For the number, choose half your total system memory, in the examples case, its for a system with 512megs ram, you should use 512000 for systems with a gig of ram.

------3-----

I had the same problem, fixed it. Edit the config.cfg file if the hl2\cfg folder and set the following.

cl_forcepreload "1"
sv_forcepreload "1"
cl_smooth "0"

The first 2 were there but set to "0", I had to add the last line.
I still get the odd tick but few and far between and it only lasts an instant.

I hope this helps a lot of people.

------4-----

If you're still getting sound stuttering, or popping, or static after the above (which should help with HD pauses, but not the sound pauses), then change the following setting in config.cfg - eliminated sound stuttering completely for me.

snd_mixahead is originally set to "0.1"

Change it to a higher number - the number will vary by PC, but for me it was:

snd_mixahead "0.5"

That'll fix it - if it doesn't, set the number higher. If you set it lower than the default setting, the popping/stuttering gets much worse,

With the above, that should fix it.