Exhaust whistle... Not woo woo

So my 98 obs whistle when I let go of the gas. I press the gas and rev a little, or a lot, and when it's derevving, if that's a word, it whistles in the end.
It's stock from header to 2nd cat. Cat back it has a wrx stock exhaust with stock muffler.
The exhaust has no leaks Except 2 little holes on the welds done. Nothing significant.
I think maybe the cats are going bad??

Thanks dooods