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