Earlier the car started fine, but after driving about 1/4 mile, the exhaust note changed. It got much deeper accompanied by a loss of power, even though the engine didn't die. Several lights on the dash came on and off and the TCS light stayed on but dimmed a bit. Also the speedometer and tachometer went to zero even though I was driving around 20 mph. I pulled over, turned it off for a minute and since, it appears to be fine. My battery is less than a year old. Any ideas?