'97 Volvo 960 makes a whirring sound when I accelerate

volvo
noises
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#1

My volvo 960 makes a high-pitched whirring sound for a couple of minutes when I accelerate. It seems to happen first thing in the morning and then when I start it up to come home after work. In other words, when the engine is cold (or as cold as it gets in Austin, Texas) My mechanic had it for 3 days and couldn’t isolate the problem. He replaced the serpentine belt on the off chance that it was causing the problem but no-go. My tachometer has stopped working as well and I suspect that the whiring sound is related to it