I just replaced the both the right and left engine mount, but for some reason I still get that deep humming moise from the right engine mount. I took the new one out and put the old one back in and the noise was gone. I then thought I might have installed the mount wrong so I removed the old one and replaced it with the new one again. Again I get the deep humming from the right mount.

Do you think I installed the left mount on the right side and the right mount on the left side? They look exactly the same. Is there a difference?