What could be the cause? There's a vibration in the gas pedal and the car hums at 1500 RPM, usually around 40 MPH. I thought maybe the throttle body was dirty, but it looks perfectly clean on the visible side. I also had the fuel injectors cleaned by Valvoline and Meineke (they cleaned the Throttle body also), and the problem still exists. By the way, Its a 2000 GLE, with 63000 miles. Ignition coils have been replaced as well. Oils changes done on time, new starter, new spark plugs, battery replaced a month or two...

Any suggestions?

I have no idea what it is but my 2000 SE does the same thing and I took it to the dealer and they told me that it was probably my oversized rims and tires. That didnt make much sense to me, but whatever. If anyone knows whats really going on here I would like to know also.

I doubt it; I have the factory 16" 5 spokes. To eliminate another factor,
I got an alignment yesterday and the problem still exists. Tomorrow, I'm getting my selonoid replaced for hesitation between 2nd and 3rd gear. Could that be cause??? Don't know, but I'll find out.

I know theres someone out there who had this problem and has fixed it.

Way too many possible causes for this kind of NVH complaint

Warped pulley(s), bad motor mount(s), tire has a bad belt...struts going out...etc.

Do you feel the vibration in the steering wheel?
If you only feel it in the gas pedal I would suspect it's driveline-related (engine, trans, CV axles) and not suspension or tires.

Well, its not really a bad vibration, its more of a deep humming sound, which has a slight vibration effect, as if the fuel injectors were dirty, but i had those cleaned along with the TB.

Maybe it lies on the line of the Transmission... I'll see what happens after getting the selonoid replaced.

Yeah, like I said the dealer checked everything out and couldn't find out what was causing it. They just blamed it on the rims and tires. It's aggravating me too, although I have not tried as many things as you have.