Noise while on reverse mode
 

I have a mazda 3GS Sedan 08 model, I already went to car dealer to check that annoying sounds while on reverse mode, according to them, they have nothing to do with that sounds, means nothing to repair, because its normal with mazda 3, I and my wife were not really convince with their answers, We feel that were not comfortable and safe to hear that annoying sounds.. by the way, i experience to hear that sounds, after the its rains, and now, we always experience that problem, any suggestions or answers about our problem... thank you in advance

I believe i am experiencing similar and also would like to hear from others if they successfully fixed this......my wife just asked me to look at her 07 mazda 3 (automatic transmission)....when you shift into reverse there is a very loud (vibration) sound (similar to a humming) . the sound lasts for approx 5 seconds then appears to die out and doesnt matter if the car is parked with brake on or driving in reverse the noise will die out . if i am in park, and I keep your foot on the brake, shift into reverse it sounds louder. When the car is running, in park, i can replicate the sound by simply pushing the car forward. (Do not hear this noise if I push the car in reverse.) I suspect the forward load i am putting a on the transmission is causing the noise and appears the transmission is the culprit ; something is vibrating more than if the transmission is in drive. I do not drive this car so unsure if this is ongoing. Today it rained, very humid and 20+ degress C....perhaps this is related to moisture as you indicated??? any help is appreciated.
anthony