Codes P1521 and P3497, intermittent rumble sound from engine?

Hello, I am having an intermittent rumbling type of sound coming from the engine, which at the moment is only within the first few minutes of starting the cold engine. It is not a "low" rumble, it is a little more of a knock-rumble sound, but it is not engine knock. It appears to be random, and is not constant, and the sound can happen while at idle or driving, but always does it only a few times and then seems to go away completely for the duration of the trip. It also does not seem to be related to engine RPM, since the "rumble" speed or volume does not increase or decrease with acceleration or slowing down and is just as likely to happen at idle.

4 days ago, I first heard this sound about 4 days ago, but that time it was while driving at a steady 40-45 MPH and was a very similar experience where it would only last 1-2 seconds at a time, and only made that rumble sound about 3 separate times and did not make the sound again that day. 2 days later the engine began surging very mildly when going a steady speed, anywhere between 45-70 MPH. They felt almost like mild shifts or soft presses of the gas pedal. Nothing extreme, but enough for my wife and I to both notice that something was going on, and after about 20 minutes of driving the Check Engine light came on and shortly after that the surging stopped for the remainder of that trip. After getting back home I got out my code reader and pulled P1521("Incorrect oil viscosity") and P3497(“Cylinder Deactivation System Bank 2”). I did some research and quickly saw that many recommended to simply change the engine oil since that alone may solve the problem of the P1521 (incorrect oil) code, and may also solve the potential MDS problem that could be related to code P3497 (cylinder deactivation), so I changed my oil and filter, 5W-20 (I have always changed my own oil, and never put in anything besides the required 5W-20).
I cleared the codes and test drove it for about 10-15 minutes just to see if I had any issues or if the CE light would come back on but did not have any drivability issues or CE light.

1 day ago, yesterday morning, starting the engine cold and then driving for a 55-mile trip, it never made the sound once and no surging. But then yesterday afternoon when traveling back home it made the rumble sound (intermittently, only 1-2 sec. At a time, maybe 6 times total) after starting the cold engine, while at idle, and then for a few minutes of driving, then went away and never came back for the entire 55+ mile trip.

Today, this morning it made the sound about 3 times, each time only about 1 or 2 seconds, and only while idling. After beginning to drive the sound did not come back.

Recap, no surging at all since changing the oil and clearing the codes, and still no CE light, so the random/weird rumble sound from the engine is the only issue at the moment.

I might be inclined to look at replacing a MDS solenoid, but I'm thinking that would not be the issue since the sound I'm hearing happens at idle, not just when driving, and the MDS system would not be engaged at idle.

Not sure if freeze frame data would be helpful, but here are some data points for that, which is with the P1521 code (apparently Dodge does not support freeze frame for more than one code). Again, the CE light has not come back on yet, but I noted the freeze frame data before I cleared the codes.
ETC: 96 degrees C
MAP (kPa): 40
RPM: 624
VSS: 0 (the strange thing about this is that the CE light came on while driving (at least 60mph), so I'm not sure how it could show vehicle speed at 0)
TP(%): 14.5
RUNTM (sec): 393 (this is another strange one. I had been driving at least 15-20 minutes, not 393 seconds.

Thank you very much for any suggestions you can offer!