It a test aircraft for a much larger Horn of Jericho. They want the Stukas to sound much meaner. The idea was conceived after opening a box of GI Cracker Jacks and getting the whistle inside...
It could've just been a very slow, incompetent worker
"Siegfried!"
"Yes Sir!"
"Why the hell is there F^%*^ pipe on your 109?"
"I found it at Gunter's workstation. "
The 109's test flight
"Gunter it is your time to shine."
"Yes sir. "
**Plane takes off and breaks up in mid flight**
"What the hell happened? "
**Looks over at Sigfried's plane with pipe**
"Oh F*ck....Sigfriend...that was part of the structure...you idiot!"
This is actually an age old question that has popped up on almost any website that deals with the luftwaffe and as far as I know there has been no answer to this question.