The car is 2000 S80 T6 with only 67k miles.

While idling (especially noticeable while in a drive thru because it echoes off the wall) there is a high pitch whine. I have no idea what it could be, it isn't audible while on the road & highway (the car is very sound proof anyways). However, you can always hear it while idling and it is getting more noticeable.

I am not a mechanic, and the only thing I can think of is the pulley tensioner because I had a Ford Taurus for a short time that developed a similiar sound and the tensioner seized on me. I believe if the S80's tensioner seizes it would destroy the engine practically because it's part of the timing belt instead of a chain, but not sure.

Any input would be appreciated & really don't want to have to replace something like the engine and we've only had the car a couple years about 19k miles. All maintenance has been done 30 & 60k mile, plus new tranny, coil pack, sensors and what not.

Thanks in advance.
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1990 740 GL 293.2k miles

It happens at idle, right? Continue through drive thru, stop, leave engine running, pull hood release, get out, open hood, use eyes and ears and powers of observation to locate the source of the whine. Listening through a rubber tube can enable you to pinpoint the sound source.
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David Hunter

The timing belt tensioner pulley is indeed a critical timing component. If it fails the belt will likely overheat and jump/shred before you realize what's happening and can shut the motor down. It will destroy the motor.
It may be a power steering or alternator bearing, drive belt pulley, water pump (or something else all together), So as suggested above it will need to be checked out by yourself or preferably a competent tech, and right away, because of the risk involved if it's the timing pulley.

One thing to consider is that the timing tensioner pulleys on these models ('99-'00) are known for premature failure. I Believe the timing belt is even sold in kit form with tensioner upgrade, and is "must" for replacement with the first timing belt. I think the service interval for the belt/tensioner on that car is 105K, but I've heard of early tensioner failures much sooner.

Don't dick around with it. Find out what the noise is. Hope it's something simple and non-threatening.
Let us know what comes of it.

Well, I used a hose to listen and the sound (if you are looking into the engine bay) comes from the left side. It is not really audible down by the alternator, but you can hear a high pitch whine sound about equally loud from both sides of the black cover on the end of the engine - which I think is the timing belt cover. I don't know if there is any other components down under or close to that area that could cause that sound, but you can hear it real well from behind the top of the black cover on the end of the engine and the front side of the black cover behind the alternator and as close as you can get to that cover.

I could give a picture diagram if it would help. I we are already short one car atm, but I guess we shouldn't drive it till we get it inspected. How much does it usually cost to replace the belt and tensioner, assuming that is where the sound is coming from.

Thanks in advance.

Congrats on your detective work. It sounds as if the timing belt idler or tensioner pulley may be on the way out. If it seizes the belt will come off, shred or break and most likely trash the engine (bent valves and more). Get it looked at very soon. When was the belt last changed?
I would not go to a dealer (much to expensive). Find an honest, competant mechanic or shop that knows and respects our Volvos. That may mean asking around a bit. Visit and talk to them, let them listen to it, ask questions, they should be able to tell you costs on the spot. I would guess parts no more than $100, labor maybe $175. Others may know better.
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David Hunter

It hasn't been changed ever. It is only at 67,000 miles.

Have you pulled out the dipstick while engine is idling? When the vent box goes it can produce a loud whining noise. Just an idea.

Would it become louder by pulling it out?... or go away?