2001 Subaru Forester (that I love) making whining noise

My car is making a sort of whining noise; it sounds like some sort of tire noise, but I checked the tires and don’t see anything that could be problematic. My husband checked to see if anything was rubbing, and doesn’t find anything. The car is quiet when it is not moving, and the noise gets somewhat louder and slightly higher-pitched as I accelerate. It almost seems like the noise changed on a different road surface, but again, I don’t see anything different with the tires. The car has about 140-150,000 on it. The noise has only been noticeable for a couple of weeks. No other problems, no change in steering or handling. No incident that I can think of that could have been a catalyst. I wanted to get some advice here before I pay my mechanic to look at it. Thanks guys!

I’m assuming, right or wrong, that the whining only occurs with the vehicle moving and is not present while sitting at idle.
Whining could mean a wheel bearing or a differential issue.

I’m also assuming the car has an automatic transmission. The final drive gear oil should be inspected and there are 2 sticks for the transmission. The final drive stick is often overlooked as it’s buried kind of down low and is located on the passenger side of the transmission near where the front halfshaft (driveaxle) enters the transmission.

Actually, it’s a manual. But yes, the noise is only when the car is moving. It is quiet at a stop. The noise doesn’t seem to be associated with shifting at all, and there has been no change in performance.

Manual or automatic, the final drive dipstick is in the same place. Make sure the gear oil level is at the full mark.
The reason why this is so critical is that what has been known to happen is that during an oil change someone may inadvertently drain the transaxle by mistake as the drain plugs are similar in appearance and are located fairly close together.

If the gear oil level is full and the whining appears to come from the front end of the car then it’s going to be a wheel bearing issue or a differential issue; preferably the former.

The problem could be due to a worn out bearing in the front belt tensioner idler wheel. Your car is at the age that can happen.