Strange 6 speed transmission squeal

[Mandingo]

Hey fellas. I have a little issue I'm hoping someone can help me with because my dealership is in denial that anything is wrong with my car.
In gears 1 through 5 my car has developed a high pitched squeal/whine that begins just under 3k rpm and it gets higher pitched all the way up to 7k rpm. This has just started and is not the normal low whine of our manual transmissions.

When I let off the gas I hear a "yeeeoww" noise and then silence until I give it gas again. There is no abnormal noise when revving the engine in neutral. The sound is just as loud with the windows down.

Other things to note:
This issue arose right after an oil change (nissan ester) ??
When revving in neutral then letting off the gas, the tach needle pauses at 1500rpm and the whole car shakes a bit.

Its annoying as hell to cruise around 3k rpm now so I've adjusted my driving habits