A squeak over bumps that started after new hangers were fitted is friction noise, and friction noise needs two surfaces moving against each other under pressure. New rubber is often slightly tacky and the metal hook is rarely smooth. As the hanger rotates, the rubber grabs and releases instead of sliding, and that stick-slip is the squeak.
Timing is the giveaway. A squeak that appears immediately after hanger work and only over bumps is not a worn bush and not a failing component. It is the interface between the new part and the old metal, which narrows the search to hooks and brackets rather than the whole suspension.
There are two interfaces: the hanger against the hook, and the hanger against its bracket. A hook squeak is high and dry and happens when the system swings. A bracket squeak is lower and happens when the body moves. Pushing down on the corner of the car tests the bracket; rocking the exhaust by hand tests the hook.
The fixes differ. A hook squeak is solved by cleaning and dressing the contact or fitting a liner. A bracket squeak is solved by checking that the hanger sits square and the bracket was not bent during fitting. A hanger twisted on its bracket squeaks continuously because it is loaded in a direction it was never designed for.
A hanger under preload squeaks far more than a neutral one, because load keeps the surfaces pressed together. Preload comes from a system that does not naturally hang where the hangers are. If the rear section had to be pulled sideways to reach a mount, every bump works that joint, and the squeak is the system trying to return.
Push the pipe in each direction at the hanger; if it springs back with force, there is preload. Loosen the joints, let the system settle and retighten, or move the hanger so the pipe hangs without being pulled. An exhaust pipe section that follows the natural line of the system never needs forcing into place.
Polyurethane hangers last longer than rubber but squeak more and transmit more noise. The harder compound does not deform as easily, so movement that rubber would absorb becomes sliding at the interface. On a road car that shows up as a squeak over bumps and a slightly harsher note at cruise.
If the squeak arrived with polyurethane, the material is the cause. The options are to accept it, to lubricate the contacts with a rubber-safe grease, or to return to rubber where movement is greatest. Do not use a petroleum-based lubricant on rubber or polyurethane; it softens the part over time and makes the problem worse.
Not every squeak is a hanger. Anti-roll bar bushes, worn lower arm bushes, a dry ball joint and even a body mount produce the same noise. Reproduce the fault without moving the car: bounce each corner by hand and listen. A hanger squeak is audible when you rock the exhaust and will not respond to bouncing the suspension.
Note also whether the squeak happens on compression, rebound or both. A hanger squeak usually happens on both because the system swings both ways; a bush squeak is often worse in one direction. That pattern plus the location usually decides whether you are chasing the exhaust or the suspension.
Clean the hook and the inside of the hanger with water, let them dry, then apply a thin film of rubber-safe grease. That alone removes most hook squeaks. Check the hanger is not twisted, the bracket is straight, and the system is not under preload. If it persists after all three, the hanger is the wrong stiffness.
There is a point where the right answer is a different hanger rather than more grease. These small parts are easy to overlook when a system is specified, but they decide whether the car is quiet over every bump. Match the hanger to the load it carries, and the other parts range covers the clips and fittings that go with the job.
