I hear a ringing in low gear going down an incline when tapping the throttle?

Hello, that noise sounds odd; I'd think engine more than transmission though, like spark knock of some kind? Have a technician near you road test the vehicle to hear the noise; they'll likely have some good experience and know how to figure out the right place to check when hearing the noise. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops