Exhaust stench in car?

[Fusion]

I get some exhaust stink inside, but only with windows down and foot off gas pedal in gear.
Anyone have an idea how to find the source?
The pass. side harness firewall hole isn't plugged, but I don't think that's where its coming from.

[CW325]

Under the shift boot there is a rubber boot. Check to see if thats ripped.

[Fleksta]

Check to see if the flange at the cat-to-midpipe is snug and/or not broken.

Mine had developed a crack there.

[Fusion]

Under the shift boot there is a rubber boot. Check to see if thats ripped.

Seems to have done the trick. Thank you.
I don't have an "upper" shift boot so I fiddled with the rubber one today and seems to have gone away. Not ripped, probably misaligned.

But I will check the exhaust, could be cracked cuz M50 pipe sags and hits everything.