Car is a 1998 S70 and it just recently started a high pitched whine from the left side of the engine compartment. The sound get louder the faster you go. sitting at idle with the hood open, nothing can be seen or heard. Any ideas???

 

If you have the tools remove the accessory belt and see fi the noise is still there by reving it.

If so try to remove the timing cover and rev it and see if it is one of the timing belt idler pulleys.

 

Okay, last time I listen to my wife's description of a car problem! I just got back from driving the car and here are the symptoms. At idle and also reving the engine, all is normal. Take it out on the highway and as you speed up, there is a low hum. As you go faster, the hum gets louder and higher in pitch. As you slow down, the sound and pitch drop down. It goes away at about 20 mph, but comes right back if you speed up. The noise appears to be coming from the left front of the car, but I am not positive of that. Any ideas??

 

Sounds like either a bad tire or Bad front wheel bearing.