There is contact, which is metal touching something else and is broadband and irregular. There is resonance, which is a boom or a buzz that appears in a narrow band and disappears outside it. And there is internal noise, which comes from inside a muffler or a resonator when something within it has come loose. Each has a different cause and a different fix.
Naming the noise correctly is most of the diagnosis. Owners describe all three the same way and then start replacing parts. A recording made from the same seat position, at a steady speed, separates them quickly: contact is random, resonance is steady and tonal, and internal noise is a flutter that follows load rather than the road.
The first question is what the noise tracks. If it appears over broken surfaces and disappears on smooth ones, the cause is contact with the body or the suspension. If it appears at a particular engine speed and holds there whether the car is moving or not, it is resonance or something internal, and the road surface is irrelevant.
Sit in the car and hold engine speed while stationary. A noise that reproduces at a standstill cannot be contact with a moving part of the chassis, which cuts the search area down immediately. If it only appears under load and never at rest, the engine is moving on its mounts under torque and closing a gap that is open when parked.
With the system cold, put a gloved hand on the pipe near each hanger and push it gently in each direction. A healthy system moves a little and comes back. A system with a problem either moves much further than expected, or stops abruptly against something, or produces the noise you have been chasing.
Push at the points where the pipe passes closest to the body, since that is where contact is most likely. If pushing the pipe changes the noise, you have found a clearance problem rather than a part failure, and the fix is a hanger adjustment or a small trim rather than a replacement. The test costs nothing and rules out most expensive possibilities.
A stainless steel exhaust muffler that buzzes at one engine speed and is quiet everywhere else is usually showing a loose internal baffle or packing that has shifted. The sound gets described as a rattle, but it behaves like a tone: it arrives, holds, and vanishes as the engine passes through.
The confirmation is that nothing external changes it. If pushing the pipe, moving the hangers and checking clearances make no difference at all, and the noise repeats at a specific load, the source is inside the can. That is a part question, and the useful evidence is a recording plus the exact conditions rather than a written description alone.
A hanger holding the pipe out of its natural position stores energy, and the system releases it as a creak or a knock when the pipe moves. The sound is usually a single knock over bumps rather than a continuous rattle, and it often appears when the car is turning, when weight shifts, or when the drivetrain rocks.
The test is to look at the rubber: a preloaded hanger is pulled to one side and its hook is not centred in the mount. Fitting a bracket or mount slightly differently, or relieving the pipe so it hangs naturally, removes the sound. Adding a second hanger to a preloaded system usually makes it worse by storing another load.
Work through it in order. Reproduce the noise at a standstill to rule out chassis contact. Push the pipe cold to test clearance. Look at the hangers for preload and off-centre rubbers. Only then consider the part itself. That sequence resolves most cases without buying anything or removing anything.
If the noise survives all three checks, repeats at a specific load, and is unchanged by moving the system, then the part is the answer and the next useful step is documentation rather than another guess. A clean recording and a note of the conditions is what turns a complaint into a diagnosis, and it is what lets anyone say something useful about it.
