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Squealing sound coming from engine compartment

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Ah it has been a bad week for the boxster. First the buzzing door locks now I have a squealing sound coming from the engine compartment.

When the car is started from cold there is no noise. After approx 15 min of driving (car up to normal operating temp 180-190) the squealing starts barely noticeable at first. It seems to start when at constant load or decreasing throttle and application of throttle will cause noise to stop. If I continue driving the squeal intensity increases until it is always there regardless of throttle position (it still changes in pitch and intensity with engine load/rpm just doesn't stop).

The squeal is present when moving and when stopped at idle so I believe this rules out wheel bearings/brakes. Also, squeal is not affected by clutch position, engaged/disengaged.

With car idling and noise present I removed fuses for both radiator fans and engine compartment fan with no effect.

I removed the inspection plate between the seats and the noise definately sounds like it is coming from the vicinity of the serpentine belt. I bought a new belt as the old one was due for replacement however before replacing the belt I warmed the car up till it started to make the squeal noise. I shut down the car and quickly removed the old serpentine belt and started the car without a belt on and let it run for a minute and it was still making the noise. I proceeded to mount the new belt with no effect. Since I have the noise with no belt I believe this rules out the idler pulleys, tensioner, alt, A/C compressor, water pump, power steering pump and slipping belt.

The car still runs well with no noticeable loss of power even when noise is present. Car idle is good, oil and coolant levels normal, and no fault lights are on.

Car is a 97 2.5 with 75k miles. I just complete the oil change two weeks ago and the old oil was clean. I am thinking my next step will be to drop the oil filter to check for metal before any further driving. Other than that I am out of ideas on what to check. Looking for suggestions



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The tendency to be quiet when cold seems to rule out expensive internal bearing surfaces.

Quiet while cold seems to point to things that 'warm up'. I can't think of anything with the catalytic converters so that seems to leave the water/heater hoses and some parts of the air intake system.

I would check the rear trunk for noises and mist around the coolant cap and overflow tank.

I really don't understand enough about Boxster Exhaust gas recirculation and intake to know where to look but it seems like a cracked throttle body, crossover pipe, etc could be a problem.

Have you checked your ODB-II codes?

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I have checked around the coolant resevoir and do not see anything wrong. Put the top in the service position and inspected everthing visible on the top of the motor (Intakes, all hoses, etc) and nothing appears out of place. I am wondering if a bad air pump (bearings) will squeal. There appears to be some form of electric pump mounted on a bracket on top of the motor on the passenger side (assuming this is the air pump) above the engine compartment fan. Can I unplug this to see if the noise goes away?

I did check the power steering fluid level and it is low, I will top up tomorrow once I have a chance to get some fluid from the dealer.

The plugs were replaced by a mechanic when they did the 60k service.

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The air pump runs after starting while cold. It usually stops as you drive off but may go on and off periodically, especially while at idle. When the car has reached normal operating temperature the pump is no longer active.

This means if your pump is running after warm up and is the source of your noise then something is keeping the pump on all of the time and the pump itself may not be the problem.

You can unplug the pump anytime but if you do it when the car is cold you will probably get a CEL during warmup. The CEL can be reset by disconnecting the battery for about a minute.

I would warm the car to normal operating temperature before unplugging the pump. This should eliminate the CEL issue.

Since the plugs were changed recently, I would re-torque them unless the noise is definately not coming from the bottom of the engine.

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