There’s a hidden track at the end of Oasis’ “The Hindu Times.” The gap is like half-an-hour.
I first noticed it when I played the CD on my computer and it said the track was 38 minutes.
Er, I meant to say “Heathen Chemistry.” “The Hindu Times” is actually the first song on the album.
I was going to mention that as well.
Although some of the empty track did have the sound of construction like table saws and drills.
Each of the blank tracks was only one second, though, so the total silence was less than two minutes.
Weird Al’s Off the Deep End album has 10 minutes of silence at the end and then a bunch of yelling for 6 seconds. Very disconcerting when you fall asleep listening to that CD!
(This is clearly a parody of the aforementioned Nirvana one)
Yeah, that one was called “High Desert Mountain Meth Lab”
The Negro Problem album with “Come Down Now” and “Repulsion (Show up Late for Work on Monday)” has a real hidden song that starts about 18 minutes (IIRC) after the last listed track.
That’s clever!
I just checked…the last track is actually 32 minutes long, so that’s about 25 minutes of silence between songs. A second-place finisher for this thread, perhaps.
I see that I’ve already been beaten, but:
I can’t find any confirmation for this (my Google-fu is weak tonight), but I seem to recall that the gap before Man from Milkwaukee on Hanson’s Middle of Nowhere being around 14 minutes.
(this is a little off topic, because it’s about vinyl, not CD’s. Plus, it’s about a comedy recording, not music.)
But the world’s best “hidden” thing on an album is—an entire extra side of a record.
Now we all know that the old vinyl records had two sides, right? But there exists one, and only one, which had three sides.
It’s Monty Python’s album, called Matching Tie and Handkerchief.
The disc was recorded with 2 sets of grooves, running parallel (concentricly, actually) alongside each other. When you put the record on your turntable, and set the needle down on the vinyl, it would fall into one of the grooves, and play the entire side of the album. You could do that again and again , and each time you had a 50% chance of hitting the same groove, and of course hearing the same material.
I know somebody who did just that,4 or 5 times in a row, laughed at all the jokes till he had them memorized. The next time, he just happened to set the needle down on the “other” set of grooves,heard totally new material-------and began wondering if he should give up smoking pot. 
I came into this thread hoping to see a mention of Matching Tie and Handkerchief, even though it wasn’t the kind of hidden track the OP was talking about.
The first time I discovered the other groove, I thought I was losing my mind. There was nothing on the jacket or disc label that indicated this. As I recall, both sides of the record were labeled as “Side 2,” but I just assumed that was an error.