I have this annoying squeaking/vibration noise coming from the left shifter/brake lever of my Sram Red.
It appears at every asphalt roughness the bike passes on.

The noise seems to go away if I hold that area firmly with my left hand.

Any suggestions on how to fix it?

Thank you!

Sometimes dry lube on the little black plastic bit on the backside of the brake lever quiets that down. Also squirt a little into the pivots for the brake lever and the shift paddle.