62k Corolla vibrates after t-belt change

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Hi my '97 Corolla only has 62k miles and I doubted the timing belt had ever been changed so I thought I would just to be sure. The car is a base model has the small 1.6 l engine, it has never been a quiet car. After changing the belt I noticed that the car seems louder, especially when warming up. It seems to vibrate but does get somewhat better as it warms up. Seems to be revving a lot more too. I think the gas mileage has dropped slightly as well. I figured I got the belt off a notch or the belt was too lose causing it to vibrate. I have now removed the cover and double checked everything twice. The only thing I can possibly figure out is if I have been using the wrong mark for TDC. The "0" kind of falls between the two notches but I'm pretty sure I have it on the correct 1 because I removed the crankshaft pulley bolt and the key way is straight up. 1 other thing, 1 time I backed up quickly and hit my tailpipe on a Large rock. It was running and sounding much like it is now (poorly) so I climbed under it and found I had pushed the muffler forward about 1-2 inches and out of it's hanger. All I had to do was pry it a little and put it back into place and everything has been fine for a year or more. Since I had jacked up the car to do the t belt I figured maybe I had disturbed the exhaust but I have checked and no such luck. I also aligned the engine at TDC before I removed the belt and did not rotate either the crank or camshaft with the belt off so I could not have bent valves.