I have a 2001 RX 300; after driving at highway speed for a few minutes I get a load noise (similar to exhaust noise) when excellerating. I checked under the car and had someone press on the pedal to rev up the engine. I don't hear anything along the exhaust system and I don't hear anything under the hood -- like a cracked exhaust manifold. Could the leak be such that it would only occur after the car is at temperature and running at highway speeds? Or does it sound like something else?
Thank you!

 

It is really tough to tell here. Exhaust noises will generally come from a few places (if it is indeed an exhaust issue):

1. Right underneath the engine, the accordion joint can crack.
2. At any of the joints along the exhaust pipe (joints held together by two 14 mm bolts), those gaskets can rot and noise can ensue
3. At weld points particularly on the resonator (fat muffler underneath the middle of the vehicle).

Particularly with 2, one often needs to have someone put it in drive in the parking lot or on a dead street to hear any issue with the joints under acceleration.

You might have to take a sound clip and post it up on youtube for us to get an idea.

Cracked exhaust manifold is kind of rare with this vehicle.

 

Thank you! I will make an examination and if that fails, I'll make the sound clip.

 

Common causes of what you're describing are: cracked manifold, hole in the flex pipe, and vibrating heat shields.