Subaru Forester Rumble/Vibrates When RPM's Low In Higher Gears?

[phabeon]

2018 Subaru Forester, 6MT

109K miles, just purchased from corner lot/used car dealer 3 weeks ago.

If i'm in 3'rd gear or higher and RPM's dip to exactly 1000-1500, car starts to vibrate like I'm driving over rumble strips. If I quickly shift back down to 2nd gear or 1st, vibration instantly stops.

No vibration otherwise, not even if I shift back to 3'rd gear or higher as long as RPM's are 1500K and up.

Any idea whats going on here or how to troubleshoot?

 

[phabeon]

turns out I was jus "lugging" it, guess the Subi is super sensitive, once I "acclimated" to its gearbox I no longer "lug" it at all, so no more vibrations.