Exhaust loud at idle

[BigMike18]

So I bought a new rear right car, muffler, and tail pipe and all the gaskets/rings and bolts replaced everything and tightened it all down. When I drive/accelerate the exhaust sounds normal but when I’m braking or just sitting at idle in drive it’s loud. But in park it’s fine. Any ideas?

 

[Warwicke36]

So I bought a new rear right car, muffler, and tail pipe and all the gaskets/rings and bolts replaced everything and tightened it all down. When I drive/accelerate the exhaust sounds normal but when I’m braking or just sitting at idle in drive it’s loud. But in park it’s fine. Any ideas?

Have someone put a rag over their hand and cover the tailpipe with the truck running. Get underneath it and find where the leak is. If there's no external leak found the muffler itself is likely to blame.