PI detectors do they have the same tell tail beeps

I'm curious if all pulse induction detectors would give the same tell tail signs (double beep). I did some tests to try learn some differences in sounds. I know that for my Gp Extreme I get a double beep when a target is either rings or money. Was this just a coincidence.
Next question, why couldn't I detect a gold chain on the surface stretched out, but when it was in a ball I could?
In addition, is there a DVD or video I can get that can help me learn what I'm hearing?

There was a video minelab did on the 3000 , Jack Lang also did some videos

PI machines will make slightly different sounds depending on the target. Different machines will also make different sounds. BUT if you are hunting for gold don't listen for a particular sound or try to 'discriminate' by the tone. Listen for a break in the threshold, not a particular sound. Sometimes gold will sound exactly like a bit of junk and sometimes junk will sound like gold.

As for the chain, when it is balled up it has a more concentrated surface area and is easier to pick up.