Narrative:

We were in VMC and the air was smooth; autopilot was on; and were climbing through FL280 when the first officer and I began to notice a rumbling sound. Our first thought was maybe a panel was open. As we climbed; the noise increased. I took the controls off autopilot and slightly added forward and aft pressure. The controls had a fluttering; rumbling and somewhat of a slight knocking feel to them. I transferred the controls to the first officer and had him check for the same thing. The first officer did experience the same fluttering; knocking; rumbling on the flight controls. We continued the climb while the first officer reviewed the QRH for possible guidance and I texted maintenance control our situation. We had a 'Q&a' with maintenance without any concrete answers to our situation. By now we leveled at FL340; and notified ATC that we'd like to maintain our present (slower) speed for an issued we might have. We then texted dispatch of situation; and checked the controls several times. It appeared to us that it had become more noticeable; and we decided if we do have a flight control issue then going faster would be ill advised. There was weather ahead along our route that would require deviations and present possible turbulence. The first officer and I discussed our options and opinions from past experience; including diverting. We agreed this seemed like more than an open panel. I called the flight attendant and asked if she could hear or feel anything unusual. She said she could feel something. (Slightly). The first officer and I had a 'gut feeling' this could be a flight control issue; and we also agreed in the interest of safety for everyone that it would be prudent to divert for further inspection. I texted maintenance/dispatch of our plan and they agreed. [The divert airport] has long runways and adequate facilities. I notified and briefed the flight attendant we are diverting; and then ran the applicable checklists/procedures. We declared an emergency with ATC and requested direct to [the airport]. As we descended through FL200-FL180 or so we noticed the flutter/rumbling sounds went away and the controls began to feel normal. We both thought the problem might then have to do with a high speed/high altitude issue on the controls. We landed and taxied to the gate without any further issues. The first officer did a walk around and found no abnormal issues; and then I did a walk around. I asked the first officer to do a flight control check from the cockpit while I observed the control surfaces outside; and I did not see anything unusual. At the gate I called maintenance; and while on a lengthy hold I had the first officer call dispatch. This situation arose without any notice and was not caused by any threats or errors that I'm aware of. One possible threat to us could have been it was the last leg of a 4-day. The first officer and I discussed and made it clear that will not be a determining factor in our decision of how to handle the situation. In situations like this you always have a sense of 'what else can we do?' what else is there to do?' there is always room for improvement in any situation. I believe the first officer and I stayed calm and aware of the entire situation even though stress was present. The first officer and I worked well together in handling the situation. By the time I talked to maintenance; operations deplaned everyone.

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Original NASA ASRS Text

Title: During climb through FL280 the crew of a EMB-145LR began to notice a rumbling; fluttering; and slight knocking in the flight controls that seemed to increase with altitude. An emergency was declared and the aircraft was diverted to a nearby airport. As they descended the abnormal condition diminished and eventually ceased.

Narrative: We were in VMC and the air was smooth; autopilot was on; and were climbing through FL280 when the First Officer and I began to notice a rumbling sound. Our first thought was maybe a panel was open. As we climbed; the noise increased. I took the controls off autopilot and slightly added forward and aft pressure. The controls had a fluttering; rumbling and somewhat of a slight knocking feel to them. I transferred the controls to the First Officer and had him check for the same thing. The First Officer did experience the same fluttering; knocking; rumbling on the flight controls. We continued the climb while the First Officer reviewed the QRH for possible guidance and I texted Maintenance Control our situation. We had a 'Q&A' with Maintenance without any concrete answers to our situation. By now we leveled at FL340; and notified ATC that we'd like to maintain our present (slower) speed for an issued we might have. We then texted Dispatch of situation; and checked the controls several times. It appeared to us that it had become more noticeable; and we decided if we do have a flight control issue then going faster would be ill advised. There was weather ahead along our route that would require deviations and present possible turbulence. The First Officer and I discussed our options and opinions from past experience; including diverting. We agreed this seemed like more than an open panel. I called the Flight Attendant and asked if she could hear or feel anything unusual. She said she could feel something. (slightly). The First Officer and I had a 'gut feeling' this could be a flight control issue; and we also agreed in the interest of safety for everyone that it would be prudent to divert for further inspection. I texted Maintenance/Dispatch of our plan and they agreed. [The divert airport] has long runways and adequate facilities. I notified and briefed the Flight Attendant we are diverting; and then ran the applicable checklists/procedures. We declared an emergency with ATC and requested direct to [the airport]. As we descended through FL200-FL180 or so we noticed the flutter/rumbling sounds went away and the controls began to feel normal. We both thought the problem might then have to do with a high speed/high altitude issue on the controls. We landed and taxied to the gate without any further issues. The First Officer did a walk around and found no abnormal issues; and then I did a walk around. I asked the First Officer to do a flight control check from the cockpit while I observed the control surfaces outside; and I did not see anything unusual. At the gate I called Maintenance; and while on a lengthy hold I had the First Officer call Dispatch. This situation arose without any notice and was not caused by any threats or errors that I'm aware of. One possible threat to us could have been it was the last leg of a 4-day. The First Officer and I discussed and made it clear that will NOT be a determining factor in our decision of how to handle the situation. In situations like this you always have a sense of 'what else can we do?' what else is there to do?' There is always room for improvement in any situation. I believe the First Officer and I stayed calm and aware of the entire situation even though stress was present. The First Officer and I worked well together in handling the situation. By the time I talked to Maintenance; Operations deplaned everyone.

Data retrieved from NASA's ASRS site as of July 2013 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.