Smell of smoke

[Frank3188]

Hi all
I have a e53 3.0d 122000 miles
When ever I give it some beans I get a burning smell coming in thru the windows
If the windows are shut I get no smell! It smells like exhaust fumes also
It doesn’t happen all of the time but if I then go back to normal driving for around 10 mins then lockdown again the smell is there! But if I do kickdown all the time I get no smell! I’ve also just had a new manifold and I’ve disconnected the webasto heater as that was draining the battery! I know people will say just don’t bother put your foot down but on slip roads it does come in very handy and when the kids can smell it can’t be any good for there little lungs
Any help much appreciated
Thanks
Frank