Exhaust rattling, makes a noise, speed slows.

Could be misfiring. Have someone (a repair garage) look at it.

Unless you can provide more info.

- what engine (size / engine code)
- what fault codes have you retrieved
- post a picture of the light that is on in the dash.

Thomas

I would be getting a mechanic to inspect the exhaust system from one end to the other and reporting any faults that need attention.