2008 Expedition downshift noise and other questions...

[amstel78]

Hello everyone, I'm new to this forum. I have a 2008 Expedition Limited. I bought it new in August of 2008 and currently have about 6500 miles on the odometer. Recently, I've noticed a buzzing noise that happens only when I downshift and only from 4th to 3rd, and when the truck is at a certain speed. I have a theory that when the downshift occurs at that certain speed, it creates some sort of harmonic that causes something metallic underneath the vehicle to vibrate for a second.

I'm trying to figure out what piece could be vibrating. Has anyone noticed anything similar in their Expedition?

Also, I live in NYC and get terrible mileage. I average around 8mpg in the city. I drove down with the family to Florida (in fact, I'm still here in Clearwater) and get anywhere from 16.5 to 17.3 mpg on the HWY. I read a thread where some owners average about 400 miles or more per tank. I was wondering what I could do to improve mileage?

 

[amstel78]

Any suggestions at all?

 

[pathologyknight]

i don't know about the noise, but 8mpg in the city! that's terrible.
i get about 15-17 in the city with my 07 EL. i get 20-22 on the hwy.

with less than 7k miles on it (you must not drive much) it may need to be broke in more?

mine is stock except for a K&N intake. i also run synth oil (mobil1) and had all the fluid changed a couple weeks ago. did the radiator, trans, front&rear diff, trans axel, and fuel filter. i just turned 42k on the odo.

 

[amstel78]

Well, I just got back from Florida. I averaged about 18 mpg, and got 445 miles per tank from full to empty with 2 gallons to spare. I'll look into replacing the intake and exhaust with freer flowing units. Hopefully that'll help.