New guy getting into driveline vibration scene

Hello Everyone

I have a 2012 Tacoma: RWD, Access cab, MANUAL 5 spd, I4

I reviewed Driveline Vibration T-SB-0008-14 and 2012 one. They specify automatic transmissions. Anyone heard of Toyota covering repairs for a MANUAL?

My situation:
Still in drivetrain warranty (bought new Jan 2013)
At 54,400k: sudden change. Truck has a deeper, throaty sound and slight rumbling (for lack of a better word) coming from below and behind driver seat. Also the sound of bearings (hell, what do I know what it is) or glass marbles clacking. Coming from same direction.
I hear this exactly as described in the TSBs.
I get to 15 mph in 1st gear, put it in 2nd, push right through 25 mph—and it’s a different animal.
Handling is the same. Just sounds and feels like it hit puberty and voice changed—and it thinks it grew a couple more cylinders.

HOWEVER
Right NOW I get a very slight vibration in floorboard—BUT nowhere else.

Questions:
Will this get worse over time?
I ask because I’m at 55,900k/a few months of drivetrain warranty left.
It’s a short window.
I wonder whether Toyota would cover me before warranty expiration…

Keeping in mind that my expertise doesn’t extend much beyond changing oil:
The TSBs seem to be addressing symptoms, but not causes.
My mechanic says something about the leaf springs is causing drive shaft angle to change. Doesn’t sound great.

I’d appreciate any info you have.
THANK YOU