CRJ200 First Officer reports RTU1 retuning itself without any input from the crew. This happened twice with both COMM and NAV radios being retuned.

Narrative

About 55 NM north of GSO; RTU 1 retuned itself to 130.07 and 129.80 on the VHF radios and 115.0/115.0 on the NAV tuner. Squawk code remained and was correct. It was noticed when we started to hear repeated calls from CLT Ramp. We thought initially that 129.8 may have been correct but found that not true when we heard further ramp calls. We called on 121.5 and got the correct frequency from Cherry Point Approach. After reestablishing comms; the Captain called maintenance who said the problem would go away when the plane was powered down. We monitored Guard on COMM 2 and put the Center frequency in pre COMM 2. The problem repeated approximately 50 NM north of CAE; approximately near the GLOVR intersection. I saw the RTU flicker and reset itself. I noticed that on the FMS the correct frequencies were maintained and it was only RTU 1 that was retuning itself. We reset again (using the frequency we had set in COMM 2 preset). Again the captain consulted maintenance. The problem did not repeat itself and we called maintenance on the ground.