Flying back from MSP last night on an ERJ-145 in 12A, which is my normal seat on the 145.
Shortly after we started the roll I noticed a nosie that could best be descrbed as an alarm clock (beeep --- beeep --- beeep --- beeep ---) that transitioned to a slow whoooooop (like an old-school fire alarm) that persisted until just after the wheels left the ground.
The flight was uneventful, and aside from passing by an NW aircraft that was closer to the aircraft than I've seen before (but appeared to be holding short) nothing else caught my attention. Pavement was wet; and the "beeping" didn't change speed as the aircraft accellerated)
Ovbiously whatever it was wasn't important -- but I've never noticed those noises before so I'm curious whatpart of the aircraft would be generating them.