high pitch sound coming from engine

[robbiey0]

hey guys... lately i have been noticing a high pitch sound from under the hood. i dnt know exactly where it is coming from... when i first start my car, i do not hear it right away. im not too positive when it actually starts.. sometimes it starts when i turn the heater on. im not too sure what it is, but i do know my coolant level is lower than the minimum. does anyone think that has anything to do with it, or how much it will cost for repairs? your help is greatly appreciated... thanks
-robbiey0

[mackuk]

What make model do you have engine size turbo etc..

Without any more info it is difficult to offer opinions

Some suggestions,

Loose v belt, leaking breather pipe, turbo bearings (unlikely), boost leak, water pump bearings.

If you post the exact engine type we may be able to offer more info.

[robbiey0]

v6 2.8L quattro NON-turboed... everything under the hood is completely stock... lateley it hasnt been happening as much... but it still does after a while.. can the changes in temp. be affecting it?

[mackuk]

When the noise starts is there anything you can do to make it go away, or does it come and go on it's own.

You said the coolant is a little low. Is it below the min, and has the engine ever overheated. If there has been an overheat in the cars history this "could" lead to piston ring problems, im not saying that's what it is, it's just a possability.

To diagnose the problem the best thing to do would be stop the car as soon as the noise starts and get under the hood. Try and work out roughtly where the noise is coming from. If for example is is coming from close to a v-belt squirt it with wd40 or similar light oil to see if the noise stops. This isn't a solution, if this cures the problem then the belt will need to be adjusted.

Another thing thats possible, and again this is a bit of a stab in the dark. You mentioned that the noise sometimes happened when the heaters where turned on. It may be a faulty alternator. I have seen similar issues on other cars. As electrical demand increases the alternator has to work a little harder. I can't explain why this causes a noise, although I have known this to happen.

Another possible cause is the power steering pump. If the PS pump gets locked with air it can cause the pump to sound different because it is pumping air and fluid, as opposed to just fluid. The physical difference makes for a different noise.

Check the power steering level, if it is low, or if you have recently had to top it up try the following....

Jack up the front of the car, please dont use just only a jack to support the vehicle, use axel stands for your safety. Dont use bricks or a substitute for an axel stand. this isn't safe and could suddenly shatter and cause the car to fall. It's common sense but i want to make it clear before I go any further. Dont mess with your safety!

Once the front wheels are securely away from the ground turn the ignition key one click to free off the steering lock. Remove the cap from the PS top up reservoir and turn the wheel from lock to lock about 20 times with the engine NOT running. What this will do is force any air in the hydrailics to rise to the top of the system. This will be visible as bubbles in the power steering reservoire. If the bubbles rise then the fluid level will drop. repeate this process a few times then top up if required. Be careful when lowering the vehicle. I recomend consulting your Audi manual. There is a good section on safely jacking the car.

Another possible cause is leaking vaccume pipes around the engine bay and breather system. The best thing you can be is visualy check them for evidence of damage. This could be cracking or splitting of the rubber hoses.

Hope this gives you some ideas, let us know how you get on.