I have a 2007 HCH with almost 2000 miles on it.

When I got in it this evening, I noticed a noise that wasn't there before. It's similar to the electric hum I hear normally when going up a big hill, but it's higher pitched and more noticeable. I don't hear it going below 15mph, or I can accelerate through it and it goes away around 30 or 40mph. But in that range, I hear it when I'm both accelerating and braking (it stops when I take my foot of all pedals). Turning off the A/C and radio makes no difference, and the battery has 5 bars of charge, so I don't know what it could be.

Any ideas what this is?

I believe this is normal and happens on every car. I hear it in my car and I first read about it on a website with a professional review of the HCH II.

Yes. I too think this is normal. We all hear some electrical noises (depending on how loud our radios are and how well we can hear).

However, It is possible that something is wrong. If you are worried about it, take it in to your dealer and have them check it out.

i think the battery charging.i hear it when im breaking and free wheeling.

Could it be the all electric mode, or is there too little battery for that?