Never really paid much attention to this before.  But sometimes on full boost my turbo sounds like a snake hissing, it sounds kinda cool but i`m sure its a sign that something isn`t quite right somewhere.  When the hissing occurs the needle on my boost gauge wobbles a tiny bit too in time with the hissing.

I was wondering whether it could be the wastegate not opening fully or there is some sort of pressure or air leak?  It only actually happens on full boost though.  It seems to be an intermittent problem also.

 

Samuel

Usually one of the boost pipes are split.  Does it sound like you have a puncture on your tyre but louder and have you lost any performance?

my tdi did this when it had a boost leak around a pipe joint. As SheffieldVRS said you probably have a split pipe or a connection has moved slightly and become dodgy.