Someone suggested taping a strain gage onto the barrel, rather than gluing it on. Without glue, the strain gage would not be able to measure any strain, but the gage would still be able to pick up any electrical noise (some people think the secondary pressure spikes are caused by ions in the powder gas or other electrical noises).
OK, so I taped a strain gage onto the breech of my 30-06. The cable was secured to the barrel in my usual fashion. When several cast bullet loads that are known to have mega spikes were shot, the taped-on gage failed to record anything on the Pressure Trace, even though the trigger level was set to "1", the lowest level.
On the other hand, I did encounter noise problems today on my Marlin 357 strain gage. This is the gun that has unshielded wires running all the way through the forearm, plus, I inadvertantly taped the PT cable so that it ran only 2" from the muzzle. There were several false triggers and bogus traces. However, this was plainly random noise and not the predictable spikes seen on the 30-06.