Been trying to figure this one out. Every time I go to turn the ac on the seems to be a knocking noise right under the hood. Ac blows nice cold air but the sound gets me worried. I checked it out and the noise seemed to come from right where the timing belt cover is by the valve cover. Car runs perfectly fine with/without ac, it/s just the noise. Anything I should get checked out or something I can do today?

 

The A/C compressor is located beneath the power steering pump in that general area. Given that the sound is heard only when the A/C is ON, I think you may have a noisy compressor, possibly due to a failing bearing or clutch mechanism.

 

Is the noise on all the time that the ac is on? Or does it come on and off periodically? Whenever the compressor engages there is a knocking noise on all cars but thats only when it engages, than you dont hear it anymore.

 

When I start driving it seems to go away. So yes, it does seem to happen periodically. Most often it will happen during idle.

 

Do you have a lot of engine shaking when the A/C engages during idling? You may want to inspect the A/C motor mount near the compressor. The rubber damper in the mount may be gone and you are hearing metal-on-metal bumping upon A/C clutch engagement.

 

I'll check it you but engine shaking is minimal. For the most part it's just the noise.

 

Yeah, still check the A/C motor mount. Trying to more precisely pinpoint the location of the noise would also help.

 

 

The camshaft gear and timing belt are located there. If you are sure that is where the noise is coming from, pop off the valve cover and the upper timing belt cover and do a careful inspection of the gear, belt, tensioner, and water pump.

 

Is it just a simple bolt off of the cover? I'll go check it out right now.