New member waste gate question

I have 2001 f250 and far as I know is stock, I have owned one before almost the same. When I drive this one I hear what I think is waste gate opening every time I let off the throttle under just moderate load, and continuous under fairly heavy load. I don't remember previos truck ever doing this. Just curious what I could check. Thanks

The truck had 165000 on it and a K&N filter so it's possible it's not stock turbo

It's called a turbo fart. The stock intake muffles the sound. With a Cai you can hear it. Totally normal.

Truck and wife's car is paid for now, so I'm hoping to start putting some money into this truck. Some suspension and good tuner to start I guess.

You will never hear the wastegate open on a 7.3L. You are likely just hearing the air go back through the intake when you let off, which is normal. If you ever start to hear a chattering noise when under moderate to heavy throttle, this is turbo surge.