Strange noises!

Started my V reg 306 HDi this morning about to set off for work and
after about 30 seconds the cars running noise actually changed from a
normal sound to a very loud dull (bad boy exhaust) noise as I set off.
It is a little frosty and damp this morning but I've never had this
before anyone got any ideas?

I've only just had a full service so...

 

Check the turbo boost pipe has not com adrift,its a big pipe about 3" in
diameter ,,somewhere between the air filter box and the inlet manifold,

Fitzy

 

I have had about two\three turbo pipe replacements so far (had car
about 4 years now) so it could well be that it seems to be a common
fault. I have to say though that it actually sounds like the exhaust
but I did notice a slight underpowered effect when I was driving it..

 

It was actually the CAT box that had snapped in two! :/

Must be all the bloody speed bumps nowadays finally took its toll,
probably be my shocks next!

Thanks for suggestions though was most helpful!