I have the same problem with a specrum GP-40 husle Musle loco. I found that the axles were rubing on the frame. I still wanted that growling noise for relisim but I removed the wheels filled the mounts with a fine round fiel. That quited the noice and reduced wear on the axles. With you Mountain check the axles if there is a line or rough on the axles fille the mounts.