Sound right before song begins on vinyl, what is it?

Could be something called "Print through".

This happens when the signal on the master tape bleeds through to the layer of tape next to it - actually recording itself on another section of tape. the new signal is very low in strength so you can only hear it during silence (before music starts playing). Cool huh? 

I remember back in the tape days, a rule of thumb was to never use fast-forward or rewind before storing your just-played tape. just let it keep playing 'till the end. Don't remember why, exactly. But it was a rule for hard-cores.