Boxster 3200 rpm vibration data collection

[octantman]

Good afternoon. I have suffered from a vibration that has gotten worse over the years and have participated in posts in the past. I have a simple question after stumbling across this information when monitoring live data from the engine sensors.

2003 Boxster, 65,000 miles, vibration since 8,000 miles. 5 speed manual, original owner, daily driver. Viration only under load.

In addition to the Durametreic software, I bought a portable Actron 9180 unit. I have observed that at a steady engine speed of about 3180 rpm the throttle closes from about 18% open to about 8% open all at once. It is at this precise moment that the vibration begins. The MAF confirms about 1/2 of the airflow, too. The ignition advance continues upward and is at about 44 degrees holding steady at this engine speed. When accelerating normally thru this rpm there is no drop in the MAF and throttle position, but there is no vibration, either. This seems to correspond to the rpm in which the resonance valve is activated which I have observed while stationary. I have not recorded higher rpms to see if/when the throttle opens again significantly at a steady rpm.

Is this action normal for the Boxster?

Do any of you with a 2004 with the dual throttle intake duct have this vibration?

If more data would be helpful I can post the Actron data and can collect what Durametric provides, there are over 100 items that can be recorded and would welcome suggestions of what to monitor.

Any assistance would be appreciated, even a confirmation that this is normal and look for another cause to the vibration, including raising the muffler as has been suggested in months past.

Thanks in advance.