This is a well-known problem with the 2005 (not '06-'07) Accord Hybrid ANC (Active Noise Cancellation) system. The problem is made worse by hot weather and A/C operation, and appears when the engine is operating in 3-cyl mode at that RPM range. What it does instead is amplify the engine vibration, not cancel it.
Read the last few posts here: Accord: V6..some vibration (not bad)..accelerating..warning lights
The mechanic "ike" describes a wire that you can splice to ground to trick the ANC unit into thinking the doors are always open, which disables the unit entirely*. This is the cheapest and quickest method (vs. replacing the unit or cutting microphones) to remove the rumbling sound you have at that RPM. I have done this <$10 fix on mine and a friend's Accord Hybrids, and your MPG will improve considerably because you are pressing the throttle and exiting 3-cyl mode to make the drone go away.
*Note that because ANC is now off, you will now hear a very faint rumble at that RPM. Road noise, talking, or quiet music will drown it out entirely.