Strange odor

A couple weeks ago I started smelling a strange odor in my truck.
Sometimes.
It smells like curry, or something similar.

I haven't noticed it much in the past few days, but today it came back strongly.

I was sitting here in near 90 degree heat so I'm idling.
The truck started getting cold and I turned up the heat in the bunk a bit.
That is when the smell came back.

I can smell it coming out of the bunk vents if the heat is on, yet not when it is turned all the way down.
And the effect is immediate, whether I turn up the heat or turn it down.
Turn down the heat and the smell is gone.
It doesn't happen in the cab, only the sleeper.

It's a 2013 Volvo.

Any ideas?

 

I first posted this in another section.

One poster suggested it might be a coolant leak that I am smelling.

 

Never had curry chicken?
So sad.

It is a spice that can be very hot to the taste.
It's actually the only spicy dish that I make, and it's to die for.

 

HEY!!
I resemble that remark!

Look where I live.