Hey guys, lately I've been trying to figure out what this noise is from my 2002 mustang v6. You can't really hear it when you first start it, but when it warms up it is really noticeable. While driving, it sounds like it gets faster and louder when I let off the gas, like someone shaking a spray paint can really fast. Any help is appreciated!

Hmm that doesn't sound like an exhaust leak. An exhaust leak sounds more like a air blowing noise... What you are describing is more like a metal banging noise and could be an exhaust hanger has broke and is rattling. Actually could be a list of things broke or going bad causing the sound. Sounds are one of the hardest things to track down especially over the Internet. Can you post a video so we can hear the sound?

Hard to tell without hearing it first hand, but here is an easy way to check for exhaust leaks:
Get a spray bottle and fill it with dish soap and water. (Heavy on the soap). Set a shop-vac on the "blow" setting. Blow air into your tailpipe (Helps to have a friend hold the hose to your exhaust, or use tape). Spray any suspect areas with your soap and water mixture. Spray joints, couplings, flanges... ect. If you have a leak, you will make a bunch of bubbles where the air is escaping. Good luck!

I just made a video of it, but I can't seem to attach it for some reason. I thought it could be the valves but my friend that put the engine in said they took back out and checked all of that because it was making the noise while he had it at the shop. Plus, I tried some Lucas just to see if it quiets down but it didn't. And the car doesn't run rough or back fires. It drives normal with no sort of hesitation. I will do the soapy water idea this weekend. Thank you!

Could be a loose heat shield. Easy fix with a large hose clamp.

May not be the exhaust. However, I would stop past a local muffler/exhaust shop and let them have a look at it. I took my daughter's car to one last week, because I couldn't find the leak. It was a rusted section near a connection to the resonator. He cut out the rusted section and welded in a new one. Cost me $50.