I know it sounds weird, but this is what i have going on.... With my air conditioner on and car is idling i hear almost a knock coming from my transmission. It will go away with the clutch pressed or the a/c off. If i rev the car up, even 100 rpm over idle it also stops. Im thinking its a throw out bearing or clutch disc problem. And it only happens with the a/c on because of the extra load placed on the clutch. Has anyone else had anything like this happen? any help would be great. Thanks in advance, Derek

 

It's probably the dual mass flywheel. The ECM tries to keep the engine idling at the same RPMs with and without the AC on, but with the AC on, there is extra load on the engine, and with the planets aligned just right, the flywheel resonates/vibrates/whatever. There's really nothing to be concerned about until the noise gets completely annoying. If the vehicle is under warrantee, you might be able to talk the dealer into replacing it.

 

Thank you! Im am 97% sure it is clutch and flywheel related, i will replace it in a few months, but everyone i know that has said it in person said the same thing, just leave it till it gets worse or just bothers me a lot. Its barely noticable but i dont like it

 

There's more to the story than what I had time for yesterday. The dual mass flywheel is a slightly flexible coupling between the engine and transmission which absorbs crankshaft variations in rotation so you don't hear transmission gears clanking around. This occurs when the tranny is in neutral and the clutch is engaged. What you are hearing (I guess) is transmission noise rather than the flywheel. However, flywheels deteriorate after time and use, and can cause the noise you are hearing also. So, the noise you are hearing can be caused by several problems: engine misfire, flywheel deterioration, transmission wear, or very light transmission oil. When you do the clutch replacement, carefully inspect the flywheel too - maybe compare it to a new one - to see if it needs replacement. Else go with a light-weight replacement single mass flywheel and endure a bit more tranny noise at idle.

 

Thanks for the help! I will be replacing the clutch kit with a exedy unit and a new flywheel as well. The engine is running fine with no miss, and the transmission fluid is less than 5k mile old green label Honda mtf.