97 Lesabre I hear a slight humm when driving

[davdogg42]

This started a couple of weeks ago on my 97 buick lesabre
when i get to about 35-40 mph i hear a humming sound from the bottom of car near rear.
Then i smelled a rotten egg smell
I figure it was the catalitic converter going bad but I wanted to make sure it was not the tranny instead
Car shifts fine but I hear that humm when I drive with the radio off
No warning light comes on .
but like I said I do smell that rotten egg every few days or so.

[imidazol97]

Originally Posted by davdogg42

This started a couple of weeks ago on my 97 buick lesabre
when i get to about 35-40 mph i hear a humming sound from the bottom of car near rear.
Then i smelled a rotten egg smell
I figure it was the catalitic converter going bad but I wanted to make sure it was not the tranny instead
Car shifts fine but I hear that humm when I drive with the radio off
No warning light comes on .
but like I said I do smell that rotten egg every few days or so.

Is the pitch of the sound the same if you increase the engine speed by accelerating or by touching the brake pedal to disengage the TCC OR does the pitch change with car speed like it's something related to tires or things rotating with the road speed.

It could be a rear wheel bearing. I would check first to see if you're hearin hum from the tire treads. How worn are the tire? How many years old? I had tires that were 6 years old and I started getting a hum--just because the treat was hardened. They had been rotated and were evenly worn. Still had about 30% of tread depth.