If it happens every single time, I think a cool test for you to try would be to get a certified dB meter and a GoPro, have your engine ready for an oil change with whatever oil you normally run, and get ready to collect some hard-to-dispute data.
1. Fire up the GoPro.
2. Set the dB meter to A-weighted average and place it exactly 1’ above the valve cover, then start your car (from cold). Let it run for 5 minutes while getting the readout on video. If you really want to be super thorough, repeat the 5-minute test at least 3 times both before and after the oil change.
3. Stop the car, perform the oil change (leave same filter in place) to Mobil 1 with the video running and without moving the dB meter.
4. Once the oil change is completed, reset the dB meter to clear the average of oil “A”. Start the car (cold again after the oil change), and let it run for 5 minutes while getting the readout on video.
5. Compare the before and after results of the two tests; if the deviation between the two measurements is less than the accuracy of your dB meter, the noise level is identical.
6. Upload the complete unedited video to YouTube to silence your critics!
This test may confirm your audible findings; however one thing to remember is that simply the frequency of the noise from your engine may be different with different oils, but not the amplitude- no one’s ear perceives sounds objectively, and is coloring the assessment, no matter who hears it. The dB meter is calibrated to evaluate all noises equally, and would give you a very good case to state both here and to Mobil if your test shows there is a difference.
Plus, if you went to this level of scientific experiment, not only would you know you weren’t “hearing things” but would also satisfy even the data hawks here that your claims were valid. Just sayin.