Exhaust smell in cabin while idling, any ideas?

Whenever I am sitting, idling and using the AC/heat from the front my cabin reeks of exhaust. There is no smoke, but I can clearly smell it coming out of the vents. Already wasted $1000 having the exhaust manifold gaskets replaced (dealer said that was the cause) but the smell is still there. Seems to be worse when using heat as opposed to the AC. The rest of the exhaust is intact, I have no idea where this could be coming from. Any ideas?

2007 Volvo 780 D12 engine. 738k miles.

 

Will do, would a leak there cause me to hear a faint high pitched whistle like sound when the turbo boosts up and when I use the engine brake? That started happening recently as well.

 

The fumes started long before the noise, the fumes made me go to the shop where they replaced the manifold gaskets. The whistling noise started shortly after that. I went back to the dealer complaining of the noise since it occurred right after they worked on it, they tore it all apart again, told me told me the noise was from an Egr that didn't get put back on right, put it back together free of charge. Sent me on my way, noise still there... So now I have the fumes and the noise, no headaches, it's not really noticeable while I'm driving. But while sitting it just reeks. And no, I don't notice any smell on me when I'm away from the truck. They mentioned the turbo gaskets and clamps too, but said nothing of them leaking.

 

Flex pipe seems to be the consensus...I'll check it out. Thanks guys.