Possible problem with transmission

today my car started “grunting” and it appears that it is coming from the transmission stick (the shifter?!). it happened while stuck in traffic and then when i was moving about 30m/h. firts time i heard it i tapped the shifter and it went away (or so i think); second time, doing about 30m/h, i had to press the stop pedal at that time and -maybe coincidentally- it went away. other info to consider:

-this is the first time that my car makes this sound

-this morning when i went from Reverse to drive the car had kind of a delay reaction and i was able to “hear the gear engaging”.

-i have an automatic transmission (L,2,D,n,P); shifter doesnt have any problem going from one gear to another one.

-there is no engine light (or any other light)

-the sound happened when stopped and when moving.

-i have not changed the transmission fluid in a while (maybe never)

any ideas?

thank you

oh and this is a toyota solara 2001 with 80k miles