If he sounded like the Mayor he was probably voiced by Dave Herman. Here's a list of all of his characters on the show, courtesy of TFM:
DAVID HERMAN
Scruffy
Larry
Dr. Ogden Wernstrom
Mayor C. Randall Poopenmeyer
Dean Vernon
Terry
Lou
Dwayne
Warden Vogel
Malfunctioning Eddie
Turanga Morris
Leg Mutant
Father Changstein El-Gamal
Rusty (1ACV05)
Robot General (1ACV05)
Robot Elder #2 (1ACV05)
Mall Salesman (1ACV06, 2ACV04)
Neptunian Store-Clerk (1ACV07)
Florp (1ACV07, 3ACV08, 4ACV18)
Fat-Bot (1ACV11)
Meidermeyer (1ACV11)
Slurms McKenzie (1ACV13)
Vet Jeffrey Grant (2ACV01, 3ACV03)
Political Debate Announcer (2ACV03)
Hemp Party Rep. (2ACV03)
Apathy Part Rep. (2ACV03)
Mine Spokesman (2ACV03)
Scoop Chang (2ACV03, 4ACV05)
Warning Skier (2ACV04)
Pet Store Man (2ACV04)
Robot Hobo #2 (2ACV04)
Decapodian Elder (2ACV05)
Mugger (2ACV06)
Past-O-Rama Car Guy (2ACV06)
ThunderCougarFalconBird Seller (2ACV07)
Fnog (2ACV08)
The Foreigner (2ACV08)
Internet Bouncer (2ACV09)
Nurse-talking Nerd (2ACV09)
Nerd #2 (2ACV09)
Nerd #3 (2ACV09, 3ACV15)
Alkazar (2ACV09)
Barrier-bot #2 (2ACV10)
Old Man (2ACV11)
Bureaucrat Grade 20 (2ACV11)
Number 1.0 (2ACV11)
The Colonel (2ACV12)
Soda Machine Robot (2ACV14, 3ACV08)
Lamp (2ACV14)
Recruiting Sergeant (2ACV17)
Hungarian Robot #2 (2ACV18)
Ghost Vladimir (2ACV18)
Project Satan (2ACV18)
Defrostee (2ACV19)
Elderly Defrostee (2ACV19)
Truck-stop Guy #2 (3ACV02, 5ACV09)
The Lord Mayor of Colon (3ACV02)
Priam (3ACV03)
Baseball Announcer (3ACV04)
Hair Robot (3ACV04, 3ACV11)
Break Dance Kid Leader (3ACV04)
Penguin Feeding Man (3ACV05)
"Go Away Tanker" Guy (3ACV05)
Queqeg (3ACV07)
Backstage Guy #1 (3ACV08)
Kirk (3ACV09)
Man with Sweetheart (3ACV09)
Roberto (3ACV11, 4ACV14, 5ACV10, 5ACV12)
Mad Hatter Robot (3ACV11, 5ACV10)
Broken Robot #1 (3ACV13)
Bend-Aid TV Announcer (3ACV13)
Garfunkel (3ACV13)
Bad Poem Hippie (3ACV13)
Chinese Dragon Monster (3ACV13)
Aged Complaining Teen (3ACV14)
Clyde Smith (3ACV15)
Picard Supporting Nerd (3ACV15)
Nappster Online Salesman (3ACV15)
Jeff Jervis (3ACV15)
Cheech Marin’s Head (3ACV15)
New New York Mets Coach (3ACV16)
Osiris 4 Slave Master (3ACV17)
Pharaoh Hamenthotep (3ACV17)
General Colin Pacman (3ACV18)
Air Force Base General (3ACV19)
Sarge (3ACV19)
Autopsy Doctor #1 (3ACV19)
Namgyal, the Sherpa (3ACV20)
Monk at Controls (3ACV20)
Cave Man Defrostee (3ACV21)
Steve Castle (aka That Guy) (3ACV21)
Stock Robot #1 (3ACV21)
Helmut Spargel (3ACV22)
Chairman Koji (3ACV22)
Singing Shrimp (3ACV22)
Genghis Khan (4ACV01)
Dr. Veins McGee (4ACV01)
Mugger (4ACV04)
Ambassador Moivan (4ACV05)
David Souter’s Head (4ACV05)
All My Circuits Director (4ACV06)
Executive Alpha (4ACV06)
Dr. Ben Beeler (4ACV07, 4ACV16)
Man Behind Door (4ACV07)
Soupy (4ACV08)
Homeopathic Medicine Doctor (4ACV08)
Pazuzu (4ACV09, 5ACV06)
Moose (4ACV09)
Huge Brain (4ACV10)
Infosphere Scanner (4ACV10)
Ambitious Young Squad Brain (4ACV10)
Welshy (4ACV11)
Former P.E. Captain (4ACV12)
Upgrade Man (4ACV14)
Crack Mansion Butler (4ACV16)
Amy’s Talking Devil Tattoo (4ACV16)
Whale Biologist (4ACV16)
Ranger Park (4ACV17)
Bigfoot (4ACV17)
Opera Announcer (4ACV18)
Ra-Ra, The Sun King (Game)
Adoy (Game)
Nude Beach Bartender (5ACV01)
Nudar (5ACV01, 5ACV02, 5ACV03, 5ACV04)
Constantine (5ACV02)
"Everybody Loves Hypnotoad" Announcer (5ACV04)
Giant Medium-Sized Ant (5ACV05)
Chu (5ACV05)
Enemabot (5ACV05, 5ACV06, 5ACV08)
Plastic Surgeon Robot (5ACV06)
British Robot (5ACV06, 5ACV07, 5ACV08)
Three-Eyed Zebra (5ACV08)
Soldier (5ACV09)
Killbot #2 (5ACV10)
Caged Nibblonian #3 (5ACV11)
Munchkin Roaster (5ACV11)
Larius (5ACV11, 5ACV12)
Frydo Reflection #2 (5ACV12)
The only character who I recall having the "oh, huh?, what" reaction I think your describing is the veterinarian (Jeffrey Grant, according to the list above) from "I Second That Emotion;" he started sputtering when Bender started talking about putting Nibbler down. That was the only time he reacted like that, however, so he might not be who you're looking for.