Question Odd fan issue


Jun 23, 2016
Got what I think is a unique situation here. Got a new case. Needed one with enough room for two 240x120mm radiators for my cpu and gpu coolers. Got a Rosewill Rise case. Cheap and easy. I made a decision up front that I didn't want the the fans drawing air through the radiators and blowing that warm air into the case so both of them are positioned such that the fans draw air through them and out of the case. One up front, and one on the top. This meant that I would need to turn the 140mm rear exhaust fan around and make it an intake. I set everything up, powered it on, and heard a whine coming from the rear exhaust fan. I figured it was just the fan, so I ordered a new one. Came in today, and I installed it. This fan has the exact same issue. My best theory here is that given that there are 5 exhaust fans and 1 large intake fan, perhaps the pressure in the case is he culprit? The rear fan doesn't make any noise if I run it at low RMP, which is how I currently have it set up. It's connected to a manual speed controller built into the case. I'd prefer to have it attached to the chassis fan power from the motherboard so I can control it with software, but I don't want to tolerate the noise. Another thing I noticed is that if I cover the intake with my hand, the fan stops making noise. I'm doing this lightly mind you, not pushing in on the grating or anything that would alter the shape of the fan or its housing even a little. Has anyone else experienced fan noise as a result of internal case pressure or similar? Perhaps some recommendations?
I count four exhaust fans - 2 each on two rads. Anyway, with only one intake fan (rear 140 mm) you do have a "negative pressure" set-up. Personally I prefer positive pressure, but ONLY becasue that can be set to reduce incidental dust intake. I don't believe a negative pressure system causes reduced air flow. However, an unbalanced system may reduce it somewhat. One intake and 4 exhaust may be unbalanced, but all the exhaust fans have restrictions (rads) that reduce their air flow, so the unbalance may be mild.

I gather the case came with that rear fan, but you replaced it. The original was connected to a case-mounted fan control of some sort, and you would prefer that the rear fan be controlled instead by a mobo header. In general I'd agree with that preference. There are a few details to make that work. IF the rear fan is 3-pin, then you MUST connect it to the right kind of mobo header, one that can use the older Voltage Control Mode (aka DC Mode), and not the new PWM Node for method of fan speed control. IF that fan is 4-pin, it is better to use PWM Mode, although it can be controlled by DC Mode if you have to. If you have questions on those ponts, post back here with exactly what model and maker of fan you have for the rear, and also mobo maker / model number. Since it is a case vent fan, you should be using a SYS_FAN or CHA_FAN header, and IF there is an option in its configuration for which temperature sensor to use, choose the motherboard (not the CPU internal) sensor.

Case internal pressure does not directly cause noise. Could be other things. If it is running full speed all the time, that may seem noisy, and that would be changed if the mobo were in control and reducing its speed. Also check for items in the air flow path near that fan and try to get a clear path. If any item in the area appears loose enough to vibrate as air passes, try to fasten it down.