Can spark plug gap influence knock...?

There's a GM TSB 03-06-04-060A saying to use iridium plugs gapped at 0.040" (instead of platiunum ones gapped at 0.060").

Does anyone know why the change...?

Dave, thanks, I'll read that link.

Quote:
Hi Dave,

Thanks for asking...

I applied TEC one time only, and it was a big improvement, altho on a hot day in slow traffic it will knock slightly.

I still need to check my plugs again, and to check my knock sensors (under the intake manifold which is tucked under the cowl-overhang; I'm waiting for a manifold gasket set; the cooling system does not pass thru the manifold, so I am thankful)...

And my Mrs makes sure to keep me busy with other things...

The 'rattle' seems to have moved from low range (1500 rpm) to mid range (2500 rpm)... it happens as you increase throttle thru low range, and it then stops as you keep increasing throttle to mid range.... I could be looking in the wrong place, but it does seem to me to be engine related... it's annoying, and I'm wondering what it is...

I have been under the car with a rubber hammer, I found this:
- the stock catback is sliding back from the Y pipe... I tightened the stock band clamp using a large breaker bar, but it is still sliding back... the Y pipe OD must have crimped, I'll expand it back out with a pipe stretcher tool;
- the O2 sensors (four) have a ring (for breathing fresh air I assume) which rattles and vibrates, but the sound it makes is very low;
- I need new motor/trans mounts, they're not broken but they're worn/soft/stretchy;
- the whole exhaust system has a very light rattle, but it doesn't seem to come from the cats;

I have been logging with the scantool every day and studying the logs; I'm logging pids like cylinder airmass to see if there's an abrupt change that may cause timing or AFR to change.

I have a Fluke color scopemeter (which I use for electronics) which I'm trying to connect up to the various sensors to take a recording when the rattle happens, but it's not so simple to figure out how to probe without puncturing wires (I'm a bit apprehensive about that) and how to run the test leads from engine bay to driver's seat;
I'm not too happy with the Fluke, it's not easy to use and the recording/playback user interface isn't very good.
I'm just about to buy a Pico Quad from AutoNerdz... 

Cheers,
Joe