Tdi sounds louder/different than normal

[Philtdi30]

Ok so my car has been parked up for 3days at work while I have been away. Got in drove home and at 1500 rpm I can hear a different engine sound to normal it's louder but not much but I know it's not right. When I say say engine sound I mean a distinctive change in tone to the norm.

Parked up once home turned radio/fans off etc

It's definitely slightly noiser sounding while sitting in the car with it just idling.

Then I sat in the back and it seems noisier in the back than the front while idling.

I can also hear the change in tone while reving past 1500 but then goes to normal.

Rev up to red line everything sounds normal as it used to.

Could it be the exhaust is blown?

Or maybe cat collapsed ?

The engine itself sounds fine only time I can hear a difference is at 1500 rpm or sitting In car at idle with windows all up etc it just sounds that bit noiser. And more so if I climb in the back seats.

Everything in engine bay looked ok. However I did notice some wet looking oil coming from top inter cooler pipe and bottom pipe looks dirty also. Not much but enough for me to notice.

Praying it's not turbo related

Car is lupo tdi sport

35k

Major service done last sept all filters oil etc

Cam belt/water pump aux belt done last month at vw dealer

Just flown through mot 2weeks ago

Car seems to drive fine with no power loss. Don't seem to be throwing out any smoke from the back etc...

Any other owners had any experience of this?

Any help info tips greatly appreciated

Thanks Phil

[Philtdi30]

Just to update

Fault found exhaust bracket snapped not far from flexi just before the cat. Hopefully get sorted this week.