What is causing loud muffler-like sound?

Do people hear your vehicle coming down the street before they can actually see it? This can be an embarrassing situation. A muffler that is suddenly noisy is often caused by the driver hitting something while on the road, damaging the exhaust system. Rust can also be a culprit of holes in the muffler, resulting in a noisy muffler which gets progressively worse as the holes get bigger.
Exhaust systems in newer vehicles may now last well over 100,000 miles without causing any concerns. But because the exhaust system is exposed to the conditions of the road, damage may occur without warning. The parts of the exhaust system that can be damaged include:

• Manifold
• Pre-catalytic converter
• Front pipe
• Catalytic converter
• Intermediate exhaust pipe
• Front muffler
• Rear exhaust pipe
• Rear Muffler

If you do hear a loud noise and you suspect it is the exhaust system, be sure to keep fresh air coming into the vehicle and don't sit in the car while it's idling. If there is a leak, carbon monoxide, a toxic gas, can get into the interior of the car. There is no distinguishing odor so it is easy to be overcome by it.
In order for your vehicle to keep running smoothly, all of its components need to be in good working order. Taking the time for regular car inspections and keeping up with needed repairs is the best way to ensure that everything is working as it should. This inspection should include the exhaust system.
"Why is my muffler so loud?" For an answer to your question, contact our ASE Certified technicians at Dependable Car Care for more information and to schedule an inspection of your exhaust system. Our auto shop proudly serves residents in the community of Ventura, CA, and the surrounding area.

Loud Noise Unknown Origin - Ask the GM Technician - GM-Trucks.com

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Jun 30, 2006 - 7 posts - ‎3 authors
I get a loud clunking, grinding noise while turning to the right only, and ... I moved the passenger side tire to the rear driver side just in case it ...

can bad wheel bearing/hub cause loud clunking noises?

www.jeepsunlimited.com/.../showthread.php?...loud-clunking-noises

Nov 12, 2009 - 14 posts - ‎6 authors
driving home, i noticed some metal clunking sounds coming from the front driversside. at ... hmmmm....if it's grinding, then probably a bearing.

Front Clunking sound when driving straight. - TDIClub Forums

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Dec 21, 2011 - I have a sporadic clunking noise from the drivers side front end. '98 jetta ... If I try to coast it gets really louder and more pronounced. ... whirring orgrinding could be several things: wheel bearing, brake pads due to a caliper ...

Quick Guide to Diagnosing Differential & Driveline Noises ...

Wheel barring or bad alignment

It very well could be the strut.
smaller chance could be the CV axle.
Also have the splash guards/heat shields checked to make sure they are all tight in place.

You did not mention the muffler which is the most important one for keeping the noise down. The cat,converter's primary function is pollution control, not noise and if you had a bad manifold you would have a racket even when you were idling. Was the muffler changed ? If not then that was probably the problem in the first place.

that is the exhaust pipe gasket . it is on the front pipe going to the exhaust manifold

I would suspect the wheel bearing, as these start to fail they tend to make more noise in one direction of load than the other.

did you check front fender liners ? sl is bad about coming lose in front .

mabey check out your transaxle underneath for looseness by trying to twist or wiggle it up down when its parked. nothing should move while its parked. since there no irregular wear on the tires you can cross off alignment parts underneath. does the transmission feel good switching gears? not an easy problem to solve

Check your cv (constant velocity joint) , It may have a big clearance which is the source of the noise when turning left or right and when 4wd is engage. Juts like front wheel drive cars, if the cv joint is with clearance it will tend to sound in the left or right turns. It is not exactly clicking sound , nmore like knocking sound , low in pitch, but not heavy.