I observed on my wife's 97 Lancer A/T GLXi, if the speed is between 45 to 75 kph there seems to b a humming sound. Tried to stop ang shift to neutral ang press accelerator and no humming is observed. Is that could be related to transmission? Just changed ATF last 70,000, and currently logged 73k+. Any idea what to chk? I brought it to Mitsu casa in Dasma, but I was told to observe it. Pls advise, ty.