The noise happens only during deceleration. Its a noise that sounds like I am running over small bumps.
Oh also its my girlfriends car and she is about 42k miles overdue for new fluid.. its black.

The problem is maybe that the car is having trouble down shifting the transmission might have a problem go to your mechanic to check it out just in case it is something serious

it could be the exhaust knocking ?

Hyundai has a technical service bulletin out to its dealerships for ur vehicle for:
*Automatic Transaxle 2-3 Shift Flare or Shift Shudder
and
*Automatic Transaxle Harsh and/or Delayed Shifts

In both cases, it is a fluid check & reset of the computer is (TCM) adaptive learning. In some instances, there is a modified TCM that needs to be reprogrammed.

The 'kickdown servo' may need to be adjusted or the 'pulse generator' may need to be replaced. A dealer can hook up to ur car & read the trouble codes in its computer. Worst case scenario, the transaxle needs to be replaced. If she is the original owner, she should have the 10yr/100,000 mile powertrain warranty. Any manufacturer is defect related to the transmission is covered.

The least expensive way to find out if a simple service would do it is to FLUSH the transmission. Make sure they do not just drain & fill because it does not get out all of the contaminated fluid. When u completely flush the system, u can use an aftermarket synthetic fluid instead of Hyundai, called Cam 2. We also add a friction modifier to the new fluid & use a special chemical when flushing. For a comparison, our Hyundai dealership charges $120.00 for the whole flush service (parts & labor).

If u do a simple drain & fill, measure how much is drained to know how much to put back in. But again, if the fluid is black, l highly recommend a complete flush because all u will be doing is contaminating the new fluid u put in with the fluid still trapped in the transaxle (which is a waste of money).

The 2003 A/T Accent takes 6.5 quarts of fluid when empty. Always check when vehicle is on, in neutral & at normal operating temperatures. Hyundai recommends a flush every 30,000 miles.