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Rattle that I can't diagnose

I drive a 2012 Honda CRV-V. When I accelerate through 25-35mph, there is a slight shudder/rattle. It ends when the transmission shifts up. It’s done the same thing for the past 20k miles (or more), hasn’t gotten worse or better, and doesn’t do it in any other gear.

Any thoughts?

where does the rattle come from? Front, rear…? Any vibration associated with it? Metal on metal, or plastic on plastic? Need more information.

This happened to me years ago in a RWD Olds, and it was a U-joint. CV joint?

It comes from the front of the car, but the entire vehicle shudders. Btw it’s a FWD and the cv boots have been inspected a few times since the shuddering started.

It’s not metal on metal or plastic on plastic. It’s more like a shimmy and shuddering that you feel through the wheel.

If the entire vehicle shudders, it’s time to have it professionally inspected. Could be wheel bearings, axle or other steering/suspension parts. Does the sound/shudder behave differently when you lightly apply the brakes as it happens?

engine rpm changes as trans shifts so it could be motor mounts or trans mount.

When did you replace the tires? If you haven’t or it has been a while, this could be an alignment issue. What does the tire tread look like?

Have you ever changed the transmission fluid? If not, do it.

There are a lot of possibilities including but not limited to a loose heat shield (yup, even FWD vehicles have heat shields), a bad motor mount, or a bad serpentine belt tensioner. Have you ever opened the hood, revved the engine, and listened? If not, you may want to try it. Just don’t stick your hands into the engine compartment unless you know what you’re doing. You could lose a finger. Your vehicle likely has a “drive by wire” throttle plate, so you’ll need a friend to rev the engine with the pedal while you listen under the hood.

You should also drive the car up on ramps and, with the engine off and the parking brake on, and, with gloves on, try shaking things, especially the exhaust system.

There is technology wherein a tech can place microphones or sensors at key points and record the vibration happening. It can provide a good sense of where the rattling is coming from.

Worn inner CV joints can cause a vibration at those speeds while accelerating or under load and go away when the accelerator is released.