Follow-up...
I will try increasing the audio cut fade time and see what happens for good or ill in practice...
--DR

This is a long shot... Have you checked to make sure all the audio sample rates are set to 48k? Maybe your problem is a sample rate conversion issue. Are all the source files at 48k?

FWIW, I'm not sure you understood how to turn off quick fades altogether:

Options->Quickfade Audio Edits

This is different than setting the fade length in Preferences. This actually turns the behavior on or off. I believe that was one of your original questions.

If you could upload 10 sec. of audio with one of the "ticks" somewhere on the internet, and also a screenshot zoomed in on the cut that is causing the "tick" someone may be able to give you more insight. It's hard to speculate (as has already been amply demonstrated in this thread) as to the cause of something we can't hear or see.

Are you sure the ticks are in the rendered video and not coming from something else like maybe the amplifier itself? This should be pretty easy to verify one way or the other.... If they're making the meters rise then they should be clearly seen in the audio when re-imported and zoomed on the time line

"I will try increasing the audio cut fade time and see what happens for good or ill in practice..."

I suspect this will solve your problem. Reducing it to 0 or close to 0 is very likely to induce the ticks that you're hearing. I'm also reasonably certain that all the other programs you've mentioned do this by default and likely don't even give you the option to change it. Vegas does have this option as it's roots are in audio.

I will try to test this for you time permitting. I suspect your problem is made worse by rendering to HDV. HDV encodes audio as mpeg-1 layer 3. It's a pretty horrid codec that could well emphasis any ticks. Apart from restoring Vegas's default fade length I'd also try rendering a short section to PCM at 48KHz and see how that sounds.

Bob.

Actually, HDV audio is encoded as MPEG-1 Layer-2 at 384Kbps. It is more error resilient than MP3 and is often used in broadcast applications.

Correct, it is layer 2. I don't know anything about how robust it is but from my experience it's none too attractive which is one reason I double head concert recordings. Less of an issue with XDCAM EX which uses PCM thankfully.

Back to the issue at hand.
I tried a quick and not too well thought out test. Somewhat hampered by not having a lot of HDV already captured.
I reduced Vegas Autofade length from 10mS to 1mS and cut together two pieces of HDV. Nothing untoward. Yes the cut doesn't sound nice at all and the PPM meters "jump".
I then switched Off Quantize to Frames and clicked Ignore Event Grouping. Then I could get a cut right at the top of a wave. I butted the previous clip's audio to that and totally removed the 1mS fade. The outcome was not noticeably worse but this probably was because the sound invovled is pretty close to pink noise (bad choice I know, I should find a LF sound at around 50Hz).

I rendered to both HDV and 16/48K wav. The HDV showed a different outcome to the wav file. The HDV showed what looks like what might be ringing preceeding the cut however it's a such a low level as to be insignificant. Given how these lossy codecs work not really a surprise.

My conclusion is that the rendering to HDV is probably irrelevant. The best guess is his problem is related to reducing the Autofade length to 1 mS. Then again we have no metrics, as I said before one man's inaudible tick can be a horrendous thump to someone else. We really need a small sample of the problem, even a screenshot of the resultant waveform would reduce the amount of speculation involved.

Bob.

Seeing as how I was on a roll with this I tried another test.

I created a 50Hz 0dBFS tone with SF. Aligned it with vision so the peaks were at frame boundaries and grouped them. I then turned QTF On and trimmed one frame. Really bad click as expected.
I changed the Autofade length back to 10mS and the result was much better but still there's an audible thump, as expected.

I'm out of ideas. I cannot break Vegas, it does exactly what I expect it to do within the bounds of how audio needs to be edited.

Bob.

[beginning with responses to my most recent post, above...]
--To John Cline: All of the clips are 48 Khz.
--To Musicvid: You are right - quick fades were not turned off in Options -> Quickfade Audio Edits. I will try this, and also try uploading a clip with the original problem in it (I have none handy now, since I fixed all I found - what a pain!).
--To Blink3times: The ticks remain at certain locations in tracks, and are not randomly located, so this is unlikely a gear-related problem (especially since the gain in the tracks are reduced to "0", with supposedly no sound at all, let alone enough to cause clipping).
--To Farss: I think you are right on all counts - I will try both removing the fades, and also increasing the fade times.
--To John Cline: Hmmm..., V E R Y interesting about MPEG-1 layer-2 being more error resilient than MP3! ;-)
--To Farss: Try taking an HDV clip with audio that has been gain-minimized using the clip "rubber band", then butted to a clip with the audio given a normal fade in (to presumably butt silence-to-silence with the two clips). Then render it. After rendering it, play the resulting clip and watch the meters carefully and listen (high-gain playback is not required to hear it...). The "tick" and meter jump are VERY brief, but VERY hard to miss (but may be hard to locate unless the rendered track is placed directly above the silenced original material so that the cut location can be easily found visually...).
--To Farss (again): Thanks for your efforts (and those of others). While we seem to be proving that the effect "should" happen (darn! ;-), the point for me is that it never has before for me with Mini-DV or HDV, using many different programs other than Vegas. There are solutions: one is the "kludgy" one I have been using of cutting out the "tick" and re-rendering; another is the more suitable one of overlapping audio tracks that are supposedly silent (I do not get "ticks" with cuts where there is non-silent audio [but I may then just not hear them], but as I noted earlier, I rarely edit with butt cuts); and another possibility is that changing audio settings in the program (either removing auto fades at cuts, or increasing their duration) may work.
Thanks, again, to all!
--DR