A rumbling sound

I notice to hear a weird sound coming from the front of car. I can tell its not engine noise. At first I thought it was tire being worn cause they were in bad shape. Then put new tires on and issue still the same. So I thought maybe transmission but shifts great and when I am going down the highway I would put in neutral and still the same sound except when slowing down I hear the sound going down. Any ideas? This is an automatic transmission.