2.0 GT TDi 170 DPF replaced - Rattling and exhaust gas issues

[seally13]

I've recently had to succumb to putting my Mk5 Golf in the garage to have the DPF replaced (140k on the clock now). It'd been going in on and off for about a year to be manually regenerated because taking it on a run wasn't clearing the DPF light and it kept putting on the EML and dropping into limp mode. When I recently took it to the garage, apparently they had to do the regen four times to clear it to an acceptable level. The last time it went in it wouldn't clear at all and so I had to bite the bullet and have the DPF changed.

When I had it changed, the mechanic told me that he'd had to reset the ECU to tell the car that it had been replaced and the car would take a bit of time to 're-learn' my style of driving before it would perform fully again. I don't know if that's right?

There have been a few occasions when driving it where the car has kangaroo'd (which is what the mechanic described it would do) but these seem to have decreased now that I have racked up some miles on it.

Since having the new DPF on the car, however, I've noticed a rattling noise coming from under the dash / bulkhead area when driving along and the engine is running at around 1200rpm (which wasn't there before). Bizarrely, it also seems that if the car is facing down a hill idling at traffic lights then the rattling also happens when revs are around 1200rpm. Any ideas what this might be?

Also, the car smells quite strongly in the cabin of exhaust fumes (especially when reversing), which it didn't before it went in to the garage.

Please can someone advise me what might have caused the rattling and the smell of exhaust gas? Could it be a coincidence or should I be taking it back to the garage for another repair?

[Renars]

Maybe new DPF or exhaust touching body of car somewhere. Need to lift up and check it.
I suppose new DPF could smell when its hot for a while since its new.