My father owns a 2006 Accord Hybrid. The car averages about 21 MPG. He drives almost 100% short trips around town so perhaps this explains the poor millage, however, he could probably get better millage out of a conventional small SUV.

However this is not the main problem. The main problem is that when driving on some road surfaces at certain speeds, the car makes a sort of "chattering" sound that hits resonance and becomes incredibly hard on the ears. Therefore, on just the right road surface at just the right speed, the whole car resonates with this loud rumble.

Has anyone else experienced this problem?

Wow, that is pretty poor FE but I suppose if the trips are REAL short, the engine barely gets warmed up (where ECO mode will begin activating). I can usually get between 29 and 32 in town with my 2007. Ask him if he sees a fairly active CHRG and ASSIST when he drives (this is also impacted by temp).

I'm not sure what's going on with the resonance road noise problem. I haven't experienced that and it makes me think something in the drivetrain system could be having a problem (might also be related to the fairly low FE). Has your dad taken the car in to be inspected?

I have spent some time driving it and it does spend a good amount of time in ECO mode and the CHRG and ASSIST remain fairly active.

The noise resonance is really weird and my father did take it in to a local mechanic who was unable to identify the problem. I had said earlier that the car was a 2006 but it is in fact a 2005. My father had signed up for the waiting list in early 2004 before the car was out and was among the first owners of the car in late 2004. Therefore, it is out of warranty, at least with respect to the non-hybrid systems, so my father is a little reluctant to take the car in, as in this area, any trip to the dealership can result in a bill for thousands of dollars with no guarantee of a successful outcome.

I also though that the noise might be tire noise, but I no longer think that because sometimes the noise occurs when the car is moving very slow, but usually it occurs when the car is just under 40 MPH, although it is not consistent. The sound appears to be coming from the middle of the car, although it is hard to tell. Once the noise starts to resonate, the whole car pulses with this sound.

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Thanks, that's my answer!

-Joe