Anyone experience having a slight vibration sounds like plastic not a metal sound like heatshield it is only Audible mostly when going uphill around 1800-2k rpm it goes away below or above it...

I experienced this when I serviced my Coolant and Thermostat but I recycled my coolant in a good way...

PS video attached I have been parked inclined for a long time that's why it's showing low oil level but my oil level is okay this one the sound is audible at 7 secs onwards at around 1k rpm... https://gemoo.com/tools/upload-video...olinkgenerator

I was hoping I can get answers from here... We already double check the bolts if there are loose or something... I was thinking to:

1. Re do the Coolant Change and change the Thermostat again
2. Maybe Engine Mounts? or Tranmission Mounts?

The tricky part here is that this vibration sound is only audible if you don't have your AC on
If you have your AC on the noise is not audible or maybe it's there but you cannot hear it
Another tricky part is for example you are driving no AC and the sound is audible and then along the way you decided to turn on your AC because you are getting annoyed it will not disappear right away like it will take may 1-2 min before it goes away permanently or the rattle/vibration sound is no longer audible..

Any inputs will do.. Thank you!