Just after fixing the previous problem, here another one!

I chose to replace "tes4title.mp3" file with a different track (changing this one's name into the original file) because I wanted a theme slightly better epic than the official one. However, whenever I launch Oblivion happens two things:

1) When the title makes the slow apparition, there is no sound:

2) When the title screen totally appears (or just when press a button), the game launch a random track on "Music" folder.

I mean, it's not a big deal when compared to the previous problem... but definitely annoying.

I hesitated to reply because I'm not a sound expert.

One potential explanation for me is that your new file is not quite compatible with the mp3 player Oblivion uses (other player, a release issue?).
To test it, you could replace the original file not with the one you'd like to hear, but with one of the files of Oblivion's music folder. What happens?

That Oblivion plays a file from the music folder instead of your file (and instead of displaying an error message or crashing the game) may be the consequence of a design decision, determining what happens, if there is a problem with playing the original title music. But I'm only guessing.

Is this original Oblivion and not the remaster?

Original Oblivion, any mp3 you put in should have a bitrate of 192kbps or lower. 256kbps *may* work, but the original music files are all encoded at 192kbps. Convert down to 192kbps and see if it then works.
I do not know if VBR vs CBR makes a difference. These are vairable vs constant bitrate. Shouldn't, but keep in mind as a test?

I do not own the remaster. It should be able to handle higher bitrates. Maybe uses OGG instead now though. But then, can't look or test it myself.