A320 first officer reported experiencing distracting headaches and fatigue from what he described as...

Narrative:

During cruise we noticed an annoying noise in the cockpit that only occurred after the aircraft leveled off in cruise flight and the auto thrust retards the thrust from climb to cruise thrust; the sounds a normal 320 engine [type] aircraft retarding the engine thrust to idle when the fans rumble temporarily.however on [this aircraft] the rumble of the unsynced fans is continuous and low frequency to the point where you feel it internally. When the [other type] engines are at full power there is no low frequency rumble; [and] when the engines are at idle; there is no low frequency rumble. But when the engines are in cruise thrust; there is a constant low frequency rumble that constantly comes in and out [and can be] heard/felt in the cockpit.when I stepped outside the cockpit to use the lavatory; both the captain and I noticed that you cannot hear the fan rumble in the passenger cabin (or at least in the forward galley/forward lav area). Upon returning to the cockpit after a lavatory break; we were subjected to the unsynced fans again.we didn't notice it during the [first] leg; but it was becoming annoying by the [second] leg and by the time we were flying [the last leg] I had a throbbing headache and I found it difficult to perform my pilot duties and concentrate on the tasks at hand.I also submitted an accompanying company fatigue report. Investigate the low frequency unsynced fan harmonics on the engines. Limit number of legs crew fly [this] aircraft.

Original NASA ASRS Text

Title: A320 First Officer reported experiencing distracting headaches and fatigue from what he described as a continuous low frequency rumble from the engines in cruise flight.

Narrative: During cruise we noticed an annoying noise in the cockpit that only occurred after the aircraft leveled off in cruise flight and the auto thrust retards the thrust from climb to cruise thrust; the sounds a normal 320 engine [type] aircraft retarding the engine thrust to idle when the fans rumble temporarily.However on [this aircraft] the rumble of the unsynced fans is continuous and low frequency to the point where you feel it internally. When the [other type] engines are at full power there is no low frequency rumble; [and] when the engines are at idle; there is no low frequency rumble. But when the engines are in cruise thrust; there is a constant low frequency rumble that constantly comes in and out [and can be] heard/felt in the cockpit.When I stepped outside the cockpit to use the lavatory; both the Captain and I noticed that you cannot hear the fan rumble in the passenger cabin (or at least in the forward galley/forward lav area). Upon returning to the cockpit after a lavatory break; we were subjected to the unsynced fans again.We didn't notice it during the [first] leg; but it was becoming annoying by the [second] leg and by the time we were flying [the last leg] I had a throbbing headache and I found it difficult to perform my pilot duties and concentrate on the tasks at hand.I also submitted an accompanying company fatigue report. Investigate the low frequency unsynced fan harmonics on the engines. Limit number of legs crew fly [this] aircraft.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1409916
Time
Date	201612
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	A320
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe

A320 first officer reported experiencing distracting headaches and fatigue from what he described as a continuous low frequency rumble from the engines in cruise flight.