Trouble shooting loud ringing sound

My 1998 Camry makes a loud ringing sound but not all the time. Once it starts, usually after the engine has warmed up, it only stops when I take my foot off the gas pedal and step on the brake. Any ideas about what is causing this ringing sound and how can I fix it? Thank you.

Have someone inspect the exhaust flex pipe under the engine. On this flex pipe is a braided stainless steel section. This braided section is clamped to the pipe with metal collars. These metal collars can corrode and break off the pipe allowing them to sit loose on the pipe. Then when the engine reaches a certain frequency these broken collars can begin to spin and ring on the pipe.

Tester

Tester is usually right, and in any case, the noise is very likely coming from somewhere along the exhaust pipe even if it isn’t the end clamps on the flexible section… I can’t recall if there are heat shields that might be rusting loose. There probably are.

Anyway, your Camry is extraordinarily low slung (people have trouble with them hanging up on speed bumps). That makes it very difficult to see the exhaust system. Do NOT yield to the temptation to slither around checking the exhaust pipe and the stuff hung off it with the vehicle supported only by a jack. Use jack stands or wheel ramps.