my 2001 chrysler sebring lately sounds really loud, especially when I get on the highway, I don't know if it's my engine or transmission but I do get my oil changed every 3,000 miles. wondering what some of the issues could be before I bring it to a shop who will most likely over price me.

Sounds are purely subjective, but here goes! I would pop the hood and listen at idle, to try and pinpoint anything unusual, like a belt, power steering pump, alternator, or ac. The fan may be running constantly, or something may be rubbing a moving part, like a wire or hose. With a partner, try giving it some engine speed while you listen for the sounds. Since you did not mention a specific sound, just a constant one, examine the exhaust system for leaks or corrosion. Joints, seals and muffler are likely after 12 years. If it occurs only while rolling, bearings, brakes or tires may be at issue. Finally, the transmission can make unusual sounds or door, top and window seals can let noise intrude over time but that would be obvious. A little detective work should reveal the cause(s). Our state requires an annual inspection, if you mention your issue, and give a tip, they might agree to look things over a bit more closely for you while on a lift.