cold start ups

[Fox_24]

On cold start ups my exhaust sounds like it has a vacuum leak. After a little bit of idling it will go away. On really cold mornings it will go away then when im driving and let my foot off the gas it will come back. When its making this sound the truck has no power and wont do over 15mph. When im idling and it goes away on its own it goes away quietly when i give it throttle in park it will make a loud popping noise.
I was told my wastegate may not be opening and closing properly but wanted to see what you guys had to say. I tried to get a video but its a little warmer today and not doing it.

[dannanw]

Exhaust Back Pressure Valve

[justinlogue5_0]

yep.

[bob harris]

yep again maybe