All City vehicles have a number posted on the front, sides, and back. Try to get the number on the truck. The truck number will identify the specific vehicle and make it possible to determine which Department and which crew is working there. If in doubt, you may contact 757-382-2489 (CITY) to inquire.
The truck may be on your street to clean sanitary sewer lines. When washing sanitary sewer main lines, air is pushed out and sucked into the system via vent stacks at the top of your house and through manhole lids. This may cause a bubbling or gurgling sound in your toilet.
If it is a box truck or a customized van, it may be inspecting the inside of the piping with a closed circuit TV camera. The crew may be inspecting more than one segment of pipe from one location. You should see proper safety cones and signs for City crews working in the street.