wilkes

That is the power supply fan, not unusual I have replaced a few of those on the GX270's because they were noisy.

It's the top one.

Someone I know has a Dell computer that has did this from the day they got it a few years ago. It sounds like it is literally going to lift off when the fan starts going. I tried to get them to take it back when they first got it but they thought it was just something it did. It has gotten worse over time.

First there are 2 fans, one is cpu fan other is power supply,the p/s fan is at the very top on 270's cpu fan is near the center. knowing which one is causing the problem will help.

All is good with the dust and heat sink. The fan just speeds up sporadically. I had a local tech tell me the power supply was going out but it's been doing this for quite sometime.

Fan my be lose. Make sure the fans heat sink is very snug on the cpu socket. If it twists or moves easily the latch is worn. You may want to replace it.

Have you ever cleaned the inside of it? It's probably getting junked up with dust, causing it to run warmer than normal.

I have a Dell Optiplex GX 270 and often the fan get's to running so fast I think it's gonna take off. Just wondering what could cause this.