Rattling when I let foot off accelerator

Howdy folks, Just bought a lemon, major odometer rollback. Anyhow, 2005 Subaru impreza outback sport 5 spd manual transmission with at least 330k on it but sold to me with 118××× and I think either a new or refurbished engine.

I’ve put about 3000 miles on it in the month ive had it and it’s been doing great (surprisingly)but recently started a rattley, clattery noise when I let off the gas. Any speed. Any gear. And the higher the rpms when I let off, the louder the noise. It has even done it once or twice at idle.

Side note p0420 engine cat code has been thrown since the monitor reset after about 200 miles from when I bought it. The battery connection was loose so I figured he reset it right before I looked at it. (Yes yes, I’m a gullible idiot I know.)

I also have a mile or so of not the best dirt road as my driveway so thinking maybe the stress of driving up and down that daily has loosened something? Taking it to a mechanic on my next day off just trying to relax about it but also trying to figure out if I’m about to spend a couple hundred bucks or cry alot and try to find a less yellow sour vehicle. At least I think I’ve learned my lesson about trusting people who are trying to sell me something.


Sounds to me like like something loose/broken in the muffler, like perhaps a heat shield. The “cat code” you mentioned could also mean you have a worn out catalytic converter, and something in there is rattling when you let off the gas.

I’d have the exhaust system inspected.


330K ? Yipes! At that mileage almost every component of the braking system would have been replaced and a good portion of the suspension as well…not to mention the drivers seat etc… I hope it doesnt have the mileage you think it does (you can check online) and or the price was low enough to warrant the purchase.

As for the rattle sound… It does sound like it could be a heat shield on the exhaust somewhere. Easy to check if you got under the vehicle and inspected the exhaust.

Certainly with that many miles and having survived one engine failure, your catalyst could be shot.

However, P0420 “Catalyst Efficiency Below Threshold” on an OBD2 engine may mean (and probably does mean) that you have at least one oxygen sensor that is old and slow to respond. My cars always throw P0420 codes long before the computer figures out that the problem is actually oxygen sensors.

If the car kills new oxygen sensors quickly, the fear would be that someone may have used liberal amounts of silicone seal when rebuilding the engine.

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Thanks y’all. I hope it’s not the cat. It probably is. Yeah def 330+ miles it was sold as 118 original owner car but og owner actually sold it to homie I bought it from with 330 and blown head gasket. He never transferred title or registered in his name so I cant even send him hate mail. I called og owner from title/reg name to figure out info. Crazy though cus the car does NOT look like it could have 300+ on it. Props to the first owner, really.