Cars - abnormal sound?

Hi,

i own a 156 1.9 JTD with 110KKm on the clock (build 1999).
Since a week or three I hear this high pitch sound whenever reaching 2000rpm
(in every gear)
I've never heard it before because I used to drive with my radio on (normal
level, I can still speak to my passenger at 120kph without having to raise
my voice, but then the radio got stolen )
Today I drove with the windows down and on the outside it sounds
more as if someone is banging with a hammer on the engine. Strangely enough,
on the inside you really have to know it the sound is there, because it's
really not that loud. Ever since I had a 33 1.7IE (don't you miss the sound
of that? :-) ), I know the sounds of my alfa-engines and this I've never
heard before. Now, I must also mention that the protective plate at the
bottom of the engine is torn and is hanging loose at the right back side.
anyway, could this have anything to do with the valves or ?????

Does anyone know this situation?

I must say, I've only had 1 problem since I bought it (injector busted)
It's been at the garage more for repairing bodywork, I've been bumped into 3
times allready, one time on the rear really bad, had to change complete rear
side. Makes a man cry if that happens...

Well, greetz to all you alfisti outthere!!!!
Kurt