Scratching squeaking noise on acceleration (solved)
 

Just posting this here for posterity

Symptoms: scratching squeaking noise upon acceleration at low rpm, especially on launch. Seemed to follow rpm only under load and could not be heard above 3k rpm.

Suspects: Bearings, pulleys, worn suspension components, worn engine/trans mount, heat shielding, actual transmission, clutch components.

Actual cause: L-shapped bracket (P/N 986 505 639 00), that is used to mount the screws at the bottom of the rear bumper, was bent forward when I refit the bumper. The bracket would then rub on my shiny new exhaust juuuust enough when I accelerated to make this puzzling noise.

Fix: bend bracket back, but be careful because there may be the end of a sharp and rusty screw sticking up through it.